Jamieson, Fausset and Brown on 1 Corinthians 11:17

17. in this--which follows.

I declare--rather, "I enjoin"; as the Greek is always so used. The oldest manuscripts read literally "This I enjoin (you) not praising (you)."

that--inasmuch as; in that you, &c. Here he qualifies his praise (1Co 11:2). "I said that I praised you for keeping the ordinances delivered to you; but I must now give injunction in the name of the Lord, on a matter in which I praise you not; namely, as to the Lord's Supper (1Co 11:23; 1Co 14:37).

not for the better--not so as to progress to what is better.

for the worse--so as to retrograde to what is worse. The result of such "coming together" must be "condemnation" (1Co 11:34).