Tertullian

What is the sign? "Behold, a virgin shall conceive and bear a son." In fact, a virgin did conceive and gave birth to "Emmanuel, God with us." This is the new birth: a man born from God. God was born in the man, taking the flesh of the old human race without the help of the old human seed. God took the flesh in order to reform the old human race with a new seed. In other words, he spiritually cleansed the old human race by removing its old stains.