When the madness of idolatry and irreligion filled the world and the knowledge of God was hidden, whose part was it to teach the world about the Father? Man's, would you say? But men cannot run everywhere over the world, nor would their words carry sufficient weight if they did, nor would they be, unaided, a match for the evil spirits. Moreover, since even the best of men were confused and blinded by evil, how could they convert the souls and minds of others? You cannot put straight in others what is warped in yourself.
Perhaps you will say, then, that creation was enough to teach men about the Father. But if that had been so, such great evils would never have occurred. Creation was there all the time, but it did not prevent men from wallowing in error.
Once more, then, it was the Word of God, Who sees all that is in man and moves all things in creation, Who alone could meet the needs of the situation. It was His part and His alone, Whose ordering of the universe reveals the Father, to renew the same teaching.
But how was He to do it? By the same means as before, perhaps you will say, that is, through the works of creation. But this was proven insufficient. Men had neglected to consider the heavens before, and now they were looking in the opposite direction.
Wherefore, in all naturalness and fitness, desiring to do good to men, as Man He dwells, taking to Himself a body like the rest; and through His actions done in that body, as it were on their own level, He teaches those who would not learn by other means to know Himself, the Word of God, and through Him the Father.
On the Incarnation, book 3
While I had always particularly favoured the section directly preceding this part, as I read this bit again I was struck by the power of it. Ah the Word.
It was the Christian teaching of man's sinfulness and total inability that convinced me Christianity was true all those years ago (and as I continue to feel the warping of such a nature, it still does). Man can't discover the knowledge of God, nor can he find God in creation. Rather, God found us in revealing to us his Word-and the Word made flesh.
And people wonder why I would be perfectly willing to name a child Athanasius :)