Do this, and thou shalt live. I have explained a little before, how this promise agrees with freely bestowed justification by faith; for the reason why God justifies us freely is, not that the Law does not point out perfect righteousness, but because we fail in keeping it, and the reason why it is declared to be impossible for us to obtain life by it is, that it is weak through our flesh, (Romans 8:3.) So then these two statements are perfectly consistent with each other, that the Law teaches how men may obtain righteousness by works, and yet that no man is justified by works, because the fault lies not in the doctrine of the Law, but in men. It was the intention of Christ, in the meantime, to vindicate himself from the calumny which, he knew, was brought against him by the unlearned and ignorant, that he set aside the Law, so far as it is a perpetual rule of righteousness.

And he said unto him, thou hast answered right,.... It is so written, and read; and this, as if he should say, is the sum and substance of the law, and what that requires men should do; wherefore,
do this, and thou shalt live; for the bare reading of it was not sufficient; though these men placed great confidence in reading this passage, or in reciting their phylacteries, of which this was a part, morning and night. Our Lord intimates by this, that, according to the tenor of the law, eternal life was not to be had without a complete and perfect performance of the duties of love to God, and to the neighbour, contained in these words; and this he suggests, in order to convict him of the impossibility of obtaining life by the works of the law, since such a performance cannot be made by man.

he said, &c.--"Right; THIS do, and life is thine"--laying such emphasis on "this" as to indicate, without expressing it, where the real difficulty to a sinner lay, and thus nonplussing the questioner himself.

Thou hast answered right; this do, and thou shalt live - Here is no irony, but a deep and weighty truth. He, and he alone, shall live for ever, who thus loves God and his neighbour in the present life.