John 1:17

17.For the Law was given by Moses. This is an anticipation, by which he meets an objection that was likely to arise; for so highly was Moses esteemed by the Jews that they could hardly receive anything that differed from him. The Evangelist therefore shows how far inferior the ministry of Moses was to the power of Christ. At the same time, this comparison sheds no small luster on the power of Christ; for while the utmost possible deference was rendered to Moses by the Jews, the Evangelist reminds them that what he brought was exceedingly small, when compared with the grace of Christ. It would otherwise have been a great hindrance, that they expected to receive from the Law what we can only obtain through Christ.

But we must attend to the antithesis, when he contrasts the law with grace and truth; for his meaning is, that the law wanted both of them. (29) The word Truth denotes, in my opinion, a fixed and permanent state of things. By the word Grace I understand the spiritual fulfillment of those things, the bare letter of which was contained in the Law. And those two words may be supposed to refer to the same thing, by a well-known figure of speech, (hypallage;) as if he had said, that grace, in which the truth of the Law consists, was at length exhibited in Christ. But as the meaning will be in no degree affected, it is of no importance whether you view them as united or as distinguished. This at least is certain, that the Evangelist means, that in the Law there was nothing more than a shadowy image of spiritual blessings, but that they are actually found in Christ; whence it follows, that if you separate the Law from Christ, there remains nothing in it but empty figures. For this reason Paul says that

the shadows were in the law, but the body is in Christ,
(Colossians 2:17.)

And yet it must not be supposed that anything was exhibited by the Law in a manner fitted to deceive; for Christ is the soul which gives life to that which would otherwise have been dead under the law. But here a totally different question meets us, namely, what the law could do by itself and without Christ; and the Evangelist maintains that nothing permanently valuable is found in it until we come to Christ. This truth consists in our obtaining through Christ that grace which the law could not at all bestow; and therefore I take the word grace in a general sense, as denoting both the unconditional forgiveness of sins, and the renewal of the heart. For while the Evangelist points out briefly the distinction between the Old and New Testaments, (30) (which is more fully described in Jeremiah 31:31,) he includes in this word all that relates to spiritual righteousness. Now this righteousness consists of two parts; first, that God is reconciled to us by free grace, in not imputing to us our sins; and, secondly, that he has engraven his law in our hearts, and, by his Spirit, renews men within to obedience to it; from which it is evident that the Law is incorrectly and falsely expounded, if there are any whose attention it fixes on itself, or whom it hinders from coming to Christ