Ephesians 5:29-30

‘For no man ever hated his own flesh, but nourishes and cherishes it, even as Christ also the church, because we are members of His body.'

A man takes great care of his own body, and nourishes and cherishes it, and he will therefore do the same for his wife who has been made one with him. So Christ does the same for His people for they have been made one with Him and are members of His body. The analogy is that just as husband and wife have been made one by the act of union, so Christ and His church have been made one, and because this is so He will nourish and care for it too.