3:19-22 If that promise was enough for salvation, wherefore then serveth the law? The Israelites, though chosen to be God's peculiar people, were sinners as well as others. The law was not intended to discover a way of justification, different from that made known by the promise, but to lead men to see their need of the promise, by showing the sinfulness of sin, and to point to Christ, through whom alone they could be pardoned and justified. The promise was given by God himself; the law was given by the ministry of angels, and the hand of a mediator, even Moses. Hence the law could not be designed to set aside the promise. A mediator, as the very term signifies, is a friend that comes between two parties, and is not to act merely with and for one of them. The great design of the law was, that the promise by faith of Jesus Christ, might be given to those that believe; that, being convinced of their guilt, and the insufficiency of the law to effect a righteousness for them, they might be persuaded to believe on Christ, and so obtain the benefit of the promise. And it is not possible that the holy, just, and good law of God, the standard of duty to all, should be contrary to the gospel of Christ. It tends every way to promote it.

21. "Is the law (which involves a mediator) against the promises of God (which are without a mediator, and rest on God alone and immediately)? God forbid."

life—The law, as an externally prescribed rule, can never internally impart spiritual life to men naturally dead in sin, and change the disposition. If the law had been a law capable of giving life, "verily (in very reality, and not in the mere fancy of legalists) righteousness would have been by the law (for where life is, there righteousness, its condition, must also be)." But the law does not pretend to give life, and therefore not righteousness; so there is no opposition between the law and the promise. Righteousness can only come through the promise to Abraham, and through its fulfilment in the Gospel of grace.