Matthew 7:12

Our Lord Jesus here presses upon us that righteousness towards men which is an essential branch of true religion, and that religion towards God which is an essential branch of universal righteousness. I. We must make righteousness our rule, and be ruled by it, Mat 7:12. Therefore, lay this down for your principle, to do as you would be done by; therefore, that you may conform to the foregoing precepts, which are particular, that you may not judge and censure others, go by this rule in general; (you would not be censured, therefore do not censure), Or that you may have the benefit of the foregoing promises. Fitly is the law of justice subjoined to the law of prayer, for unless we be honest in our conversation, God will not hear our prayers, Isa 1:15-17; Isa 58:6, Isa 58:9; Zac 7:9, Zac 7:13. We cannot expect to receive good things from God, if we do not fair things, and that which is honest, and lovely, and of good report among men. We must not only be devout, but honest, else our devotion is but hypocrisy. Now here we have, 1. The rule of justice laid down; Whatsoever ye would that men should do to you, do you even so to them.

— Matthew Henry's Concise Commentary (public domain)

Therefore--to say all in one word. all things whatsoever ye would that men should do to you, do ye even so to them--the same thing and in the same way. for this is the law and the prophets--"This is the substance of all relative duty; all Scripture in a nutshell." Incomparable summary! How well called "the royal law!" (Jam 2:8; compare Rom 13:9). It is true that similar maxims are found floating in the writings of the cultivated Greeks and Romans, and naturally enough in the Rabbinical writings. But so expressed as it is here--in immediate connection with, and as the sum of such duties as has been just enjoined, and such principles as had been before taught--it is to be found nowhere else. And the best commentary upon this fact is, that never till our Lord came down thus to teach did men effectually and widely exemplify it in their practice. The precise sense of the maxim is best referred to common sense. It is not, of course, what--in our wayward, capricious, gasping moods--we should wish that men would do to us, that we are to hold ourselves bound to do to them; but only what--in the exercise of an impartial judgment, and putting ourselves in their place--we consider it reasonable that they should do to us, that we are to do to them.

— Jamieson-Fausset-Brown Commentary (public domain)