For what great thing or what sign should have been in this, that a young woman conceiving by a man should bring forth,—a thing which happens to all women that produce offspring? But since an unlooked-for salvation was to be provided for men through the help of God, so also was the unlooked-for birth from a virgin accomplished; God giving this sign, but man not working it out. On this account
Irenaeus of Lyons
Against Heresies, Book III
Chapter XXI