Jamieson, Fausset and Brown on 1 Corinthians 11:20

20. When ... therefore--Resuming the thread of discourse from 1Co 11:18.

this is not to--rather, "there is no such thing as eating the Lord's Supper"; it is not possible where each is greedily intent only on devouring "HIS OWN supper," and some are excluded altogether, not having been waited for (1Co 11:33), where some are "drunken," while others are "hungry" (1Co 11:21). The love-feast usually preceded the Lord's Supper (as eating the Passover came before the Lord's Supper at the first institution of the latter). It was a club-feast, where each brought his portion, and the rich, extra portions for the poor; from it the bread and wine were taken for the Eucharist; and it was at it that the excesses took place, which made a true celebration of the Lord's Supper during or after it, with true discernment of its solemnity, out of the question.