A.T. Robertson Commentary 1 Corinthians 11:28

"But let a man prove himself, and so let him eat of the bread, and drink of the cup." — 1 Corinthians 11:28 (ASV)

Let a man prove himself (δοκιμαζετω ανθρωπος εαυτον). Test himself as he would a piece of metal to see if genuine. Such examination of one's motives would have made impossible the disgraceful scenes in verses 20f..