Ephesians 5:27-28

and to present her to himself as a radiant church, without stain or wrinkle or any other blemish, but holy and blameless. In this same way, husbands ought to love their wives as their own bodies. He who loves his wife loves himself.

(v27-28, NIV)

Jesus cleanses the church in order that he can present the church to himself. He wants a church that is holy and blameless, so he cleanses the church by the washing with water through the word. In the same way husbands, don't you want your wife to be holy and blameless? Lead in righteousness and cleanse her. She is your wife, why would you want your wife to be dirty with blemish? This comes from an outpouring of love we have for our wives. Husbands are to love their wives as their own bodies. In doing so, they love themselves.

For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh.

(Genesis 2:24, NIV)

Husband and wife are both one flesh. They join together in marriage to become one. So, when the husband loves the wife, he loves himself, because they are both one flesh.