Now a mediator is not a mediator of one, but God is one.
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Ambrosiaster
AD 400
Without doubt, a mediator, that is, arbiter, is not of one but two. For when two peoples were contending against one another, always at odds and enemies because of the disparity in their doctrines, the Savior came as their Mediator, taking from each people the cause of discord so that they might be at peace. So he took from the Gentiles the plurality of gods and cult of the elements, and he took from the Jews the works of the law, that is, new moons, circumcision, the keeping of the sabbath, the distinction of foods and other things that the Gentiles abhorred. And thus those who were formerly enemies came to be at peace. If then this is the case, how could the Galatians be so dullwitted as to violate this reconciliation by conversion back to Judaism? Epistle to the Galatians–.
Now a mediator is not a mediator of one, but of two, in this case of two peoples, Jews and Gentiles, to whom Christ acts as mediator, says Ambrose. (2.) Or, Christ is not a mediator of one nature, but of two, the Divine and the human. (3.) Or, Moses is not a mediator of one will and purpose, because as a man he was subject to change. God on the contrary is unchangeable in His will and promise. Adam leans to this explanation. But all these are beside the phraseology of Scripture and the drift of the Apostle.
(4.) A better interpretation is that Christ is a mediator not of one but of two—not of two Gods, as though Father and Son make two, according to the heresy of Arius and Nestorius—not between God and angels, for the good angels need no mediator, and the evil angels cannot derive any benefit from one—but He is a mediator between the two parties, God on one side and man on the other. And the inference drawn is that it is not the law, but Christ, that redeems us and reconciles us to Go...
What can the heretics say to this? For as, according to them, the expression the Only True God excludes the Son from being true God, so here the phrase God is One, excludes Him from being God in any sense. But if, although the Father is called One God, the Son is nevertheless God, it is very plain that though the Father is called Very God, the Son is very God likewise. Now a mediator, says he, is between two parties; of whom then is Christ the Mediator? Plainly of God and of men. Observe, he says, that Christ also gave the Law; what therefore it was His to give, it is His to annul.
