Verses 15–16: Spoken self-exclusion does not equal reality
The foot and the ear each claim non-belonging because they are not a hand or an eye (1 Corinthians 12:15). Paul’s implied rebuttal is that such a claim does not make it true.
Verse 17: A single-function body is impossible
If the whole were an eye, hearing would be absent; if the whole were hearing, smelling would be absent. The illustration makes functional diversity a necessity.
Verses 18–20: Many members, one body
God is presented as the one who arranged the members in the body. If all were one member, “body” would cease to exist; therefore the present reality is many members yet one body.