Augustine of Hippo

The inquirer, then, might say that the prophet says only that Christ is God, without any reference to his human nature. Yet, in our apostolic doctrine, Christ is not only God in whom we may safely trust but also the mediator between God and humankind—the man Jesus. The prophet explains this in the words in which he seems to check himself, and to supply the omission: "The heart," he says "is inscrutable above all things, and he is man, and who shall know him?" He is man in order that, in the form of a servant, he might heal the hard in heart and that they might acknowledge as God him who became man for their sakes, that their trust might be not in humankind, but in God—man.