John Calvin Commentary 1 Corinthians 12:19

"And if they were all one member, where were the body?" — 1 Corinthians 12:19 (ASV)

If all were one member: He means that God has not acted randomly, or without good reason, in assigning different gifts to the members of the body. He did so because it was necessary for the body's preservation. For if this symmetry were taken away, there would be utter confusion and derangement. Therefore, we ought to submit ourselves more carefully to the providence of God, which has so suitably arranged everything for our common advantage. One member is taken here to mean a mass that is all of one shape and not distinguished by any variety; for if God were to fashion our body into a mass of this kind, it would be a useless heap.