(18) 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.

Verse 18. - Partakers of the altar. It is better to render it "Have they not communion with the altar?" for the word is different from that in the last verse. The meaning is that, by sharing in the sacrifices, the Jews stood in direct association with the altar, the victims, and all that they symbolized (Deuteronomy 12:27). And St. Paul implied that the same thing is true of those who sympathetically partook of idol offerings.

10:15-22 Did not the joining in the Lord's supper show a profession of faith in Christ crucified, and of adoring gratitude to him for his salvation ? Christians, by this ordinance, and the faith therein professed, were united as the grains of wheat in one loaf of bread, or as the members in the human body, seeing they were all united to Christ, and had fellowship with him and one another. This is confirmed from the Jewish worship and customs in sacrifice. The apostle applies this to feasting with idolaters. Eating food as part of a heathen sacrifice, was worshipping the idol to whom it was made, and having fellowship or communion with it; just as he who eats the Lord's supper, is accounted to partake in the Christian sacrifice, or as they who ate the Jewish sacrifices partook of what was offered on their altar. It was denying Christianity; for communion with Christ, and communion with devils, could never be had at once. If Christians venture into places, and join in sacrifices to the lust of the flesh, the lust of the eye, and the pride of life, they will provoke God.Behold Israel after the flesh,.... So the apostle calls them, to distinguish them from the Israel of God, the spiritual Israel, whether Jews or Gentiles; who are born again, believe in the true Messiah, worship God in a spiritual manner, rejoice in Christ Jesus, and have no confidence in fleshly things; but these were the descendants of Jacob or Israel by carnal generation, were carnal men, in the flesh, in a state of unregeneracy, and were employed in a carnal worship, in the observance of carnal commandments and ordinances; these the apostle directs to, to see, consider, and take notice of what they were doing; from whence some instruction might be taken, for the further clearing of the present point:

are not they which eat of the sacrifices partakers of the altar? yes, they are. The priests and Levites who waited at the altar, and ministered about holy things there, who brought the sacrifices and laid them upon the altar of the burnt offerings, where the altar consumed and devoured one part by fire, and that which was left they ate among themselves; and so as they had communion with one another in eating, they partook of the altar, of the things, or sacrifices of the altar, and showed themselves to be of the Jewish religion, and professed and declared that they worshipped the God of Israel, and would be thought to have communion with him in so doing; in like manner, such who eat of things sacrificed to idols, declared themselves to be idolaters, to be of the Pagan religion, to be worshippers of idols, and to have fellowship with them.