In Augustine’s time, as now, the doctrine of the Virgin Birth was under sustained attack. The key difference is that, in his time, the enemies of the doctrine did not often claim to be Christians. Here is a choice selection from William Griffin’s translation of Augustine’s sermons for festival days:
So what do the so-called Wise and Prudent think of this great miracle? Well they prefer to think of it as a nice story rather than a hard fact. So, when it comes to Christ’s appearing as man and God–clearly a divine consideration–they run into trouble. They think it beneath them to believe that there are things that aren’t human; that there are in fact things that are divine. Hence, they see no reason why they can’t condemn the existence of the divine altogether. To them it’s just plain embarrassing that God should walk around in a silly, ill-fitting body. To us, of course, it’s a genuinely encouraging sight. To put it another way, which’ll trully appear perverse to the Unwise and Imprudent, the more impossible the virgin birth of a human being appears to them, the more divine it seems to us.