3:20 Now a mediator is not [a mediator] of one, {24} but God is one.
(24) A taking away of an objection, lest any man might say that sometimes by consent of the parties which have made a covenant, something is added to the covenant, or the former covenants are broken. This, the apostle says, does not come to pass in God, who is always one, and the very same, and like himself.
3:20 Now a mediator is not [a mediator] of one. A mediator implies two parties between whom he acts.
But God is one. The idea is that when God makes a promise by his sovereign power no mediator is required. God acts alone. Thus it was when the promises were made to Abraham. God, too, is One, the same, always, and hence the law is not due to a change of the divine mind.
3:20 Now the mediator is not a mediator of one - There must be two parties, or there can be no mediator between them; but God who made the free promise to Abraham is only one of the parties. The other, Abraham, was not present at the time of Moses. Therefore in the promise Moses had nothing to do. The law, wherein he was concerned, was a transaction of quite another nature.
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.
