Difference is the basis for the order in things. If there were no differences between things, there could be no order between them. The very idea of order includes within it the concept of priority and of posteriority, and hence, of difference and inequality. In fact, that very separateness, i.e., the distinctions among things, is the principle of all order.1

God makes creatures unequal.

God made difference and inequality in all creatures. As Ecclesiasticus teaches:
Why does one day excel another, and one light another, and one year another year...? By the knowledge of the Lord they were distinguished.
Chapter 33, verses 7-8.
Therefore, just as God’s Wisdom is the cause of His making all creatures, so His Wisdom is the cause of Him making creatures unequal.2 By making some creatures inferior to other creatures, the whole of creation is more perfect than it otherwise would be.3

Inequality between individual persons

All men are equal in some ways. For example, they are equal before the law, so that their rights as citizens are the same despite differences between them such as in height, in wealth, etc.
However, God made persons unequal in many ways and intends this inequality. God made persons unequal in eyesight, mental acuity, natural prudence, athletic ability, beauty, musical talent, health, height, and in many other ways. God intends these inequalities.
All mankind is bound together with duties to help those individuals who are more in need of help because of these natural inequalities. So, a person who can see, can guide a blind man across the street, a taller person might reach something on a high shelf to help a shorter person.
Among all other inequalities between persons, some persons are naturally less prudent than some other persons. These less prudent persons need to be helped and protected for their own good, including protecting them from their own imprudence. There are many examples of this. For example, for their own good, civil laws prohibit persons from making contracts which include interest charges greater than a statutory maximum interest rate.4 These laws and many other laws, are ways that society protects those persons against their own imprudence, because they are less able to protect themselves.

Differences between men in society

As explained above, the very idea of order includes within it the concept of priority and of posteriority, and hence, of difference. In fact, that very separateness, i.e., the distinctions among people, is the principle of all social, political, economic, military and religious order, since difference is a principle of order. For example, in a proper military order, an army cannot have all generals or all privates. The army cannot have all equipment operators or all cooks. Etc.
St. Paul emphasizes that God made men unequal and made them to have different roles, strengths and weaknesses. Here are St. Paul’s words:
For as the body is one, and hath many members; and all the members of the body, whereas they are many, yet are one body, so also is Christ. For in one Spirit were we all baptized into one body, whether Jews or Gentiles, whether bond or free; and in one Spirit we have all been made to drink. For the body also is not one member, but many. If the foot should say, because I am not the hand, I am not of the body; is it therefore not of the body? And if the ear should say, because I am not the eye, I am not of the body; is it therefore not of the body? If the whole body were the eye, where would be the hearing? If the whole were hearing, where would be the smelling? But now God hath set the members every one of them in the body as it hath pleased Him. And if they all were one member, where would be the body? But now there are many members indeed, yet one body. And the eye cannot say to the hand: I need not thy help; nor again the head to the feet: I have no need of you. Yea, much more those that seem to be the more feeble members of the body, are more necessary. And such as we think to be the less honorable members of the body, about these we put more abundant honor; and those that are our uncomely parts, have more abundant comeliness. But our comely parts have no need: but God hath tempered the body together, giving to that which wanted the more abundant honor, that there might be no schism in the body; but the members might be mutually careful one for another. And if one member suffer anything, all the members suffer with it; or if one member glory, all the members rejoice with it.
1 Corinthians, 12:12-27 (emphasis added).
As St. Paul shows us, God did not make every man to play whatever role that man chooses. Some men are made more honorable members of society, some, less. Some men are made the “eyes” of the collective group and some are made the “feet”. Id.
St. Paul emphasizes that these differences between men give rise to the obligation that “the members might be mutually careful one for another”. Id.

God intends differences and inequalities between groups as well as between individuals.

Just as God intends the countless inequalities between individuals, He also fully intends the inequalities between different groups/peoples/ethnicities/tribes. To take a few of countless examples:
God intends all these natural differences, both the strengths and the weaknesses.
Pope Leo XIII assures us that “there will ever be differences and inequalities of condition in the State. Society cannot exist or be conceived of without them.” Rerum Novarum, §34.
These differences between one people and another, are differences between the members of society on a larger scale. St. Paul teaches us that these differences oblige “the members [to be] mutually careful one for another”. 1 Corinthians, 12:25.
All peoples and groups are bound together with duties in justice and charity. Some peoples are more capable of leading and other peoples need more guidance, more protection and need to be led because of these natural inequalities that God Wills.
These inequalities include that some peoples are naturally less prudent and don’t guide themselves and others as well as other peoples do. Such peoples need to be helped and protected for their own good. A striking example of this need occurred in Colombia, after the Masonic revolution in the early 1800s:
The liberal revolutionary governments wanted to decrease the authority of the Catholic Church and to enact land “reforms”, including the abolition of the somewhat-feudal system governing the lives of the Indians (who comprised about one-third of the population).
The previous (Spanish) government had protected these Indians (like Medieval serfs were protected) by restricting their ability to freely sell the plots of land which they possessed and farmed. In the name of freedom and the free market, the new liberal government allowed the Indians to sell their little plots of land. Rich, unscrupulous men quickly induced most of the Indians to (naïvely and shortsightedly) sell their little plots, thus ruining the small amount of independence the Indians had enjoyed. Within a few years, the ownership of the Indians’ lands was concentrated in the hands of a few rich and powerful families. The Indians became landless tenants. The land which had been cultivated by the Indians was then mostly used for grazing cattle.
Quoted from: Latin America: A Sketch of its Glorious Catholic Roots and a Snapshot of its Present, by the Editors of Quanta Cura Press, p.111, © 2016.
In light of the natural inequalities between peoples, and because the men of society are bound together in justice and charity, persons and peoples more capable of leading have a duty to guide and protect those who are less capable.
It denies reason and these natural inequalities between peoples, to insist that a society’s or an organization’s leaders would be subject to “quotas” and include a “sampling” of “everybody”, i.e., representatives from each different group or people. This is as foolish as insisting that a basketball team must fulfill “quotas” and have members who “represent” every people in proportion to every part of the public.

God’s intent that there be inequality in society includes His intent that there be economic inequality (viz., rich and poor).

The revolutionaries in society stir up discontent by complaining there is an “income gap” between the rich and the poor, or that this income “gap” is increasing. However, an inequality in economic conditions is a natural reflection of other inequalities between men. God Wills these inequalities.
Quoting earlier Doctors of the Church, St. Thomas explains that God Wills wealth inequality for both the rich and the poor, so that the rich might acquire the virtue of liberality and so that the poor might acquire the virtue of patience. Here are his words:
The temporal goods which God grants us, are ours as to the ownership, but as to the use of them, they belong not to us alone but also to such others as we are able to succor out of what we have over and above our needs. Hence Basil says [*Hom. super Luc. xii, 18]: “If you acknowledge them,” viz., your temporal goods, “as coming from God, is He unjust because He apportions them unequally? Why are you rich while another is poor, unless it be that you may have the merit of a good stewardship, and he the reward of patience? It is the hungry man’s bread that you withhold, the naked man’s cloak that you have stored away, the shoe of the barefoot that you have left to rot, the money of the needy that you have buried underground: and so you injure as many as you might help.” Ambrose expresses himself in the same way.5
The Socialists seek to abolish private property, pretending that men are equal and that private property destroys this supposed equality. Here is how Pope Leo XIII explains this truth:
Socialists proclaim the right of property to be a human invention repugnant to the natural equality of man ....6
The Catholic Church, however, recognizes that all men are unequal and their differences in wealth proceeds from their many natural inequalities. Here is how Pope Leo XIII explains this truth:
[T]he Church, much more properly and practically, recognizes inequality among men, who are naturally different in strength of body and of mind; also, in the possession of goods, and it orders that right of property and of ownership, which proceeds from nature itself ....7
Pope St. Pius X condemned the false idea that:
every inequality of condition is an injustice, or at least, a diminution of justice. Here we have a principle that conflicts sharply with the nature of things, a principle conducive to jealousy, injustice, and subversive to any social order.8

Conclusion

God made creatures different and unequal. God made all men different and unequal to each other. God made the peoples and groups of society different and unequal. God intends that we help each other in our deficiencies and not that we try to impose a false equality and quota system so that all roles in society would be composed from “every group”.
  1. Here is how St. Thomas Aquinas, greatest Doctor of the Church, teaches this important point, quoting Aristotle:
    As the Philosopher says (Metaph. v, text. 16), the terms “before” and “after” are used in reference to some principle. Now order implies that certain things are, in some way, before or after. Hence wherever there is a principle, there must needs be also order of some kind.
    Summa, IIa IIae, Q.26, a.1 respondeo.↩
  2. Here is St. Thomas Aquinas’ fuller explanation of this truth:
    [I]t must be said that as the wisdom of God is the cause of the distinction of things, so the same wisdom is the cause of their inequality. This may be explained as follows. A twofold distinction is found in things; one is a formal distinction as regards things differing specifically; the other is a material distinction as regards things differing numerically only. And as the matter is on account of the form, material distinction exists for the sake of the formal distinction. Hence, we see that in incorruptible things there is only one individual of each species, forasmuch as the species is sufficiently preserved in the one; whereas in things generated and corruptible there are many individuals of one species for the preservation of the species. Whence it appears that formal distinction is of greater consequence than material. Now, formal distinction always requires inequality, because as the Philosopher says (Metaph. viii, 10), the forms of things are like numbers in which species vary by addition or subtraction of unity. Hence in natural things species seem to be arranged in degrees; as the mixed things are more perfect than the elements, and plants than minerals, and animals than plants, and men than other animals; and in each of these, one species is more perfect than others. Therefore, as the divine wisdom is the cause of the distinction of things for the sake of the perfection of the universe, so it is the cause of inequality. For the universe would not be perfect if only one grade of goodness were found in things.
    Summa, Ia, Q.47, a.2 respondeo (emphasis added).↩
  3. Here is St. Thomas Aquinas’ fuller explanation of this truth:
    It is part of the best agent to produce an effect which is best in its entirety; but this does not mean that He makes every part of the whole the best absolutely, but in proportion to the whole; in the case of an animal, for instance, its goodness would be taken away if every part of it had the dignity of an eye. Thus, therefore, God also made the universe to be best as a whole, according to the mode of a creature; whereas He did not make each single creature best, but one better than another. And therefore, we find it said of each creature, “God saw the light, that it was good” (Genesis 1:4); and in like manner of each one of the rest. But of all together it is said, “God saw all the things that He had made, and they were very good” (Genesis 1:31).
    Summa, Ia, Q.47, a.2, ad 1.↩
  4. Here, for example, is a prohibition of excessive interest, taken from New York’s civil code of law:
    4. Except as otherwise provided by law, interest shall not be charged, taken or received on any loan or forbearance at a rate exceeding such rate of interest as may be authorized by law at the time the loan or forbearance is made, whether or not the loan or forbearance is made pursuant to a prior contract or commitment providing for a greater rate of interest, provided, however, that no change in the rate of interest prescribed in section fourteen-a of the banking law shall affect (a) the validity of a loan or forbearance made before the date such rate becomes effective, or (b) the enforceability of such loan or forbearance in accordance with its terms, except that if any loan or forbearance provides for an increase in the rate of interest during the term of such loan or forbearance, the increased rate shall not exceed such rate of interest as may have been authorized by law at the time such loan or forbearance was made.
    Quoted from the 2012 New York Consolidated Laws, General Obligations, Article 5 - CREATION, DEFINITION AND ENFORCEMENT OF CONTRACTUAL OBLIGATIONS
    Title 5 - (5-501 - 5-531) INTEREST AND USURY; BROKERAGE ON LOANS
    5-501 - Rate of interest; usury forbidden.↩
  5. Summa, IIa IIae, Q.32, a.5, ad 2.↩
  6. Encyclical, Quod Apostolici muneris, Dec. 28, 1878, Denz. 1851. Here is the longer quote from Pope Leo XIII:
    But also, Catholic wisdom most skillfully provides for public and domestic tranquility, supported by the precepts of divine law, through what it holds and teaches concerning the right of ownership and the distribution of goods which have been obtained for the necessities and uses of life. For when Socialists proclaim the right of property to be a human invention repugnant to the natural equality of man, and, seeking to establish a community of goods, think that poverty is by no means to be endured with equanimity; and that the possessions and rights of the rich can be violated with impunity, the Church, much more properly and practically, recognizes inequality among men, who are naturally different in strength of body and of mind; also in the possession of goods, and it orders that right of property and of ownership, which proceeds from nature itself, be for everyone intact and inviolate; for it knows that theft and raping have been forbidden by God, the author and vindicator of every right, in such a way that one may not even look attentively upon (i.e., covet) the property of another, and “that thieves and robbers, no less than adulterers and idolators are excluded from the kingdom of heaven” [cf. 1 Cor. 6:9f.].
    Encyclical, Quod Apostolici muneris, Dec. 28, 1878, Denz. 1851.↩
  7. Encyclical, Quod Apostolici muneris, Dec. 28, 1878, Denz. 1851.↩
  8. Here is the longer quote from Pope St. Pius X, condemning the ideas of a liberal and modernist group called the Sillon:
    Teaching such doctrines, and applying them to its internal organization, the Sillon, therefore, sows erroneous and fatal notions on authority, liberty and obedience, among your Catholic youth. The same is true of justice and equality; the Sillon says that it is striving to establish an era of equality which, by that very fact, would be also an era of greater justice. Thus, to the Sillon, every inequality of condition is an injustice, or at least, a diminution of justice. Here we have a principle that conflicts sharply with the nature of things, a principle conducive to jealously, injustice, and subversive to any social order. Thus, [according to the claims of the Sillon] Democracy alone will bring about the reign of perfect justice! Is this not an insult to other forms of government which are thereby debased to the level of sterile makeshifts?
    Quoted from the encyclical sometimes called, On the Sillon and sometimes called Our Apostolic Mandate.↩