Now an intermediary implies more than one, but God is one.
20. Now, a mediator is not a mediator of one. Some are disposed to philosophize on this expression, and would make Paul’s meaning to be, that the twofold nature of Christ is not one in essence. But that Paul is here speaking of the contracting parties, no man of sound judgment entertains a doubt.
The apostle having just before been speaking of the promise made to Abraham, and representing that as the rule of our justification, and not the law, lest they should think he did too much derogate from the law, and render it altogether useless, he thence takes occasion to discourse of the design and tendency of it, and to acquaint us for what purposes it was given.
Commenting on Galatians 3:19-29
Now a mediator is not a mediator of one,.... A mediator supposes two parties he stands between, and these at a distance from, or disagreeing with each other; where there is but one party, there can be no need of, nor any reason for, a mediator; so Christ is the Mediator between God and men, the daysman, Job 9:33, that lays his hands upon them...