John Chrysostom

"If the whole body were an eye, where were the hearing? If the whole were hearing, where were the smelling?" Thus, because, having fallen upon the difference of the members, and having mentioned feet, and hands, and eyes, and ears, he led them to the consideration of their own inferiority and superiority: see how again he consoles them, intimating that so it was expedient: and that their being many and diverse, this especially causeth them to be a body. But if they all were some one, they would not be a body. …

Homily on 1 Corinthians 30 ↗

Theophylact of Ohrid

Since he mentioned the eye and the foot, the ear and the hand, and presented them as reasoning about elevation and degradation, and through this the Corinthians would naturally again come to grief rather than consolation, he now shows that it is useful and necessary for the gifts to be diverse. For if the whole body were one member, where would the rest of the members be? Are you not ashamed to reject so many members and exalt only yourself?

Commentary on 1 Corinthians ↗

Thomas Aquinas

Then when he says, If the whole body were an eye, he proves by leading to two awkward conclusions, the first of which is the removal of necessary things from the body; the second is the removal of bodily completeness (v. 19). In regard to the first he does two things: first, he presents the awkward conclusion which follows, saying: If the whole body were the eye, which is a nobler member, where would be the hearing, i.e., the organ of hearing. …

Commentary on 1 Corinthians ↗