St. Chrysostom joins the course of the discourse in this way: “The Apostle passes to a stronger example, and not only this, but to one nearer and clearer, and to a new reason. For the former did not seem very necessary. So that no one might say, ‘He was Christ, He was God, and He gave Himself,’ the Apostle proves the same thing in another way, saying: ‘So ought men to love their wives as their own bodies.’ Therefore this is not mercy, but duty.”
What follows from the obligation to love one’s wives as one’s own bodies is self-evident.
“But how is the wife the husband’s flesh? Listen: ‘Behold now,’ Adam says, ‘bone of my bones and flesh of my flesh’ (Gen 2:23). Eve is flesh from Adam’s flesh” (St. Chrysostom).
The Apostle does not set forth this foundation here, assuming it is known. Whoever knows how woman first came to be cannot be perplexed as to how the wife is the husband’s body.
The foremother Eve was taken from the forefather Adam, and Adam directly defined her by saying, “Behold, flesh of my flesh.”
What was then accomplished physically is later accomplished morally between husband and wife according to the law established by God.
After marriage, the husband has the wife in his feeling as a part of himself. The wife has herself, in her own feeling, grafted to the husband.
Thus it truly comes about that the two are one flesh, that is, one being, one person.
The Apostle speaks as though saying: there is no need to teach you how to love your wife. Love her as a part of yourself.
Of course, love for the wife requires sacrifices, as appeared above from the indication of Christ the Lord’s relation to the Church. But these sacrifices are not directed outside yourself, but toward yourself.
“He who loves his wife loves himself.” Therefore he who sacrifices something for his wife sacrifices it for himself.