For the body does not consist of one member but of many. If the foot should say, “Because I am not a hand, I do not belong to the body,” that would not make it any less a part of the body. And if the ear should say, “Because I am not an eye, I do not belong to the body,” that would not make it any less a part of the body. If the whole body were an eye, where would be the sense of hearing? If the whole body were an ear, where would be the sense of smell? But as it is, God arranged the members in the body, each one of them, as he chose. If all were a single member, where would the body be? As it is, there are many parts, yet one body. —1 Corinthians 12:14-20 ESV
John Piper comments in a sermon, “Body Pains: Feelings of Uselesness”
So Paul’s remedy for feelings of uselessness in the body is first to say that they are feelings or opinions that do not accord with truth. They are out of sync with reality (vv. 15–16). Second, to think that you should be like others in the body rather than having a unique function of your own is to go against the very idea of a body made up of many diverse members (vv. 14, 19–20). Third, and most important, resenting your gifts and your unique manifestation of the Spirit is a way of not trusting God. Since verse 18 says he put all the parts where they are with their unique functions, to say that you are useless is to say that God is weak or mistaken or evil: he is not sovereign, not wise, or not good. Like all issues it comes down to a radically God-focused issue—do you trust God?