What does 1 Corinthians 12:15 mean?

Perhaps the question the Corinthians had asked Paul about spiritual gifts (1 Corinthians 12:1) had to do with why some received more prestigious gifts while others received less desirable ones. After correcting their understanding of how and why the Holy Spirit distributes gifts to Christians, Paul began building an illustration to help believers understand more fully the point of these gifts. The church is like a body. It is one thing with many different parts—different "members"—which serve many different functions. No matter how diverse it is, however, it is still just one organism, and the health of every part is affected by the health of any individual part.

Paul now makes use of his illustration to demonstrate how ridiculous it is for Christians to complain about which spiritual gifts they have been given. Or to claim they are not a functional member. Or for them to opt out of the church because they don't like the function they serve. It would be absurd for a foot to claim it's not really part of the body because it's not a hand!

This analogy speaks to the concept of design: it's not up to the foot to make that decision, and the foot has a purpose, one that the hand is not able to correctly fulfill.