Marriage 2.4.13

But you say: “Whatever parents they are born from, we do not deny that they are still under the devil unless they are born again in Christ.” Show, then, what the devil recognizes as his own in the sexes, through which he can rightfully possess their offspring, as you say. Is it the difference between the sexes? But that is in the bodies God made. Their union? But it is vindicated as much by the privilege of God’s blessing as by his institution. For God’s voice says: “A man will leave his father and mother and cling to his wife, and the two will be one flesh” (Genesis 2:24). God’s voice says: “Increase and multiply and fill the earth” (Genesis 1:28). Or perhaps it is fruitfulness itself? But fruitfulness is the reason marriage was instituted.