Charles Ellicott Commentary Galatians 3:20

"Now a mediator is not [a mediator] of one; but God is one." — Galatians 3:20 (ASV)

The mention of the word “mediator” implies a contract to which there are at least two parties. But where there is a contract, there must also be conditions, and if these conditions are not observed, the entire agreement falls to the ground. Such was the Law. The Law was not kept, and therefore the blessings attached to it were forfeited. On the other hand, the promise depends upon God alone. He gave it, and He will assuredly keep it, no matter what humans may do. God alone is concerned in it.

This passage is a conspicuous instance of the advance that has been made in New Testament exegesis. It is said to have received as many as 250 or 300 (according to another estimate, even 430) interpretations, but at present, there is a tendency to acquiesce in the interpretation given above, which, it is hoped, will be considered satisfactory.

Now a mediator is not a mediator of one.—The very idea of a mediator involves at least two parties. The Law had a mediator; therefore, the Law involves two parties. In other words, it is a contract.

But God is one.—On the other hand, God, the giver of the promise, stands alone; therefore, the promise is not a contract; and, resting on God, it is indefeasible.