And further, submit to one another out of reverence for Christ.
For wives, this means submit to your husbands as to the Lord. For a husband is the head of his wife as Christ is the head of the church. He is the Savior of his body, the church. As the church submits to Christ, so you wives should submit to your husbands in everything.
For husbands, this means love your wives, just as Christ loved the church. He gave up his life for her to make her holy and clean, washed by the cleansing of God’s word. He did this to present her to himself as a glorious church without a spot or wrinkle or any other blemish. Instead, she will be holy and without fault. In the same way, husbands ought to love their wives as they love their own bodies. For a man who loves his wife actually shows love for himself. No one hates his own body but feeds and cares for it, just as Christ cares for the church. And we are members of his body.
As the Scriptures say, “A man leaves his father and mother and is joined to his wife, and the two are united into one.” This is a great mystery, but it is an illustration of the way Christ and the church are one. So again I say, each man must love his wife as he loves himself, and the wife must respect her husband. (Ephesians 5:21-35, NLT)
So, if that's the picture in the Bible, citing marriage between a man & a woman as a "great mystery" that gives us a picture of the relationship of Christ & His church... should it really be a surprise that redefining marriage is problematic to some of us?