Note 2 at 1Co 10:18: Paul was referring to the Old Testament practice of the priests eating a portion of the sacrifices that were offered on the altar (Le 6:18, 29, 7:6, 11-15, 8:31; and Nu 18:9-11). In doing so, they were doing more than just eating food; they were illustrating spiritual truths (1Co 9:13-14). No one was allowed to eat of the offerings but the tribe of Levi.

These Corinthian believers understood and accepted this practice. Yet, if they attached significance to the Jewish priests and their food offerings to the Lord, it was inconsistent not to recognize that there is significance in offering food to idols. This prompted Paul's statement in 1Co 10:19 that an idol is nothing and food offered to idols is nothing. But there is a communion between those who offer food to idols and the demons behind the idols (1Co 10:20). Therefore, these believers didn't need to participate.