In What Manner Many Sought the Mediator
67 Whom could I find to reconcile me to You? Was I to solicit the angels? By what prayer? By what sacraments? Many striving to return unto You, and not able of themselves, have, as I am told, tried this, and have fallen into a longing for curious visions, and were held worthy to be deceived. For they, being exalted, sought You by the pride of learning, thrusting themselves forward rather than beating their breasts, and so by correspondence of heart drew unto themselves the princes of the air, the conspirators and companions in pride, by whom, through the power of magic, they were deceived, seeking a mediator by whom they might be cleansed; but none was there.
For the devil it was, transforming himself into an angel of light. And he much allured proud flesh, in that he had no fleshly body. For they were mortal, and sinful; but Thou, O Lord, to whom they arrogantly sought to be reconciled, art immortal, and sinless. But a mediator between God and man ought to have something like God, and something like man; lest being in both like man, he should be far from God; or if in both like God, he should be far from man, and so should not be a mediator.
That deceitful mediator, then, by whom in Your secret judgments pride deserved to be deceived, has one thing in common with man, that is, sin; another he would appear to have with God, and, not being clothed with mortality of flesh, would boast that he was immortal. But since “the wages of sin is death,” this has he in common with men, that together with them he should be condemned to death.
Source: Confessions (New Advent)