Charles Ellicott Commentary 1 Corinthians 10:18

"Behold Israel after the flesh: have not they that eat the sacrifices communion with the altar?" — 1 Corinthians 10:18 (ASV)

Behold Israel after the flesh—i.e., Israel in its merely human aspect, not the spiritual Israel (Romans 2:28; Galatians 4:29; Galatians 6:16). The sacrifice was divided—a portion offered upon the altar and a portion taken and eaten (Deuteronomy 12:18; Deuteronomy 16:11): so whoever ate a portion of the same sacrifice was a partaker in common with (not “of,” as in the English translation) the altar. This is another argument against partaking of the heathen feasts. You cannot do so without connection with the heathen altar. The example of Israel proves that.