1 The words which we have sung must be rather hearkened to by us, than proclaimed. For to all men as it were in an assemblage of mankind, the Truth cries, “If truly indeed justice ye speak, judge right things, you sons of men”. For to what unjust man is it not an easy thing to speak justice? Or what man if questioned about justice, when he has not a cause, would not easily answer what is just? Inasmuch as the hand of our Maker in our very hearts has written this truth, “That which to yourself you would not have done, do not do to another.” Of this truth, even before that the Law was given, no one was suffered to be ignorant, in order that there might be some rule whereby might be judged even those to whom Law had not been given. But lest men should complain that something had been wanting for them, there has been written also in tables that which in their hearts they read not.
For it was not that they had it not written, but read it they would not. There has been set before their eyes that which in their conscience to see they would be compelled; and as if from without the voice of God were brought to them, to his own inward parts has man been thus driven, the Scripture saying, “For in the thoughts of the ungodly man there will be questioning.” Where questioning is, there is law. But because men, desiring those things which are without, even from themselves have become exiles, there has been given also a written law: not because in hearts it had not been written, but because you were a deserter from your heart, you are seized by Him that is everywhere, and to yourself within art called back.
Therefore the written law, what cries it, to those that have deserted the law written in their hearts? “Return ye transgressors to the heart.” For who has taught you, that you would have no other man draw near your wife? Who has taught you, that you would not have a theft committed upon you? Who has taught you, that you would not suffer wrong, and whatever other thing either universally or particularly might be spoken of? For many things there are, of which severally if questioned men with loud voice would answer, that they would not suffer.
Come, if you are not willing to suffer these things, are you by any means the only man? Do you not live in the fellowship of mankind? He that together with you has been made, is your fellow; and all men have been made after the image of God, unless with earthly coverings they efface that which He has formed. That which therefore to yourself you will not have to be done, do not do to another. For you judge that there is evil in that, which to suffer you are not willing: and this thing you are constrained to know by an inward law; that in your very heart is written.
You were doing somewhat, and there was a cry raised in your hands: how are you constrained to return to your heart when this thing you suffer in the hands of others? Is theft a good thing? No! I ask, is adultery a good thing? All cry, No! Is man-slaying a good thing? All cry, that they abhor it. Is coveting the property of a neighbour a good thing? No! Is the voice of all men. Or if yet you confess not, there draws near one that covets your property: be pleased to answer what you will have.
All men therefore, when of these things questioned, cry that these things are not good. Again, of doing kindnesses, not only of not hurting, but also of conferring and distributing, any hungry soul is questioned thus: “you suffer hunger, another man has bread, and there is abundance with him beyond sufficiency, he knows you to want, he gives not: it displeases you when hungering, let it displease you when full also, when of another's hungering you shall have known. A stranger wanting shelter comes into your country, he is not taken in: he then cries that inhuman is that city, at once among barbarians he might have found a home.
He feels the injustice because he suffers; thou perchance feel not, but it is meet that thou imagine yourself also a stranger; and that thou see in what manner he will have displeased you, who shall not have given that, which thou in your country will not give to a stranger.” I ask all men. True are these things? True. Just are these things? Just. But hear ye the Psalm. “If truly therefore justice ye speak, judge right things, you sons of men.” Be it not a justice of lips, but also of deeds. For if you act otherwise than you speak, good things you speak, and ill you judge.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)