Christian stuff tends to be grounded in natural law, so a lot of it is justified by things the Biblical speaker observes in nature or normal human interaction.

So, Ephesians 5:22, in the New Testament of the Bible works like this:

It claims that man and wife become one flesh (otherwise, they aren't "one entity" and there is de facto no marriage). And then it says men should love their wives as much as they love their own bodies (as that is now effectively the same thing). Then it explains what this husbandly loving means "for no one ever hated his own flesh, but nourishes and cherishes it". And then it says, "and women should respect their husbands".

So, why would you risk your life for your wife's body's sake?

Because you would risk your life for your own body's sake. You would fight back, if attacked, and try to save yourself.

Why should a wife treat her husband respectfully?

Because she treats herself respectfully. If she loves herself, she will have "standards".

We are simply being asked to do the thing we would naturally be inclined to do for ourselves, for the other person. Since men generally have more physical and/or economic power, those are the things he can offer. Since women generally have more status and/or social power, those are the things she can offer.

So that each person is made whole in the joining of the flesh. Then both of them enjoy all things, as a team.