Literally, Paul asks his readers to consider Israel according to the flesh.
This is a way of distinguishing the nation of Israel from the true Israel, which consists of all people who belong to Christ.
Paul’s use of a rhetorical question indicates that the Corinthians are well aware of the sacrificial customs in Israel.
The Israelites concluded their sacrificial ceremonies with a feast that was held in the temple courts. At this feast, they would eat the meat that was not consumed on the altar or given to the priests.
Since the meat at such a feast was sacrificial meat, it made of the eaters participants in the altar.
It was as if they sat at God’s table, enjoying fellowship with him (see Deuteronomy 12:5–7, Deuteronomy 12:11–12, Deuteronomy 12:17–18, Deuteronomy 12:26–27). Therefore, only those who were ritually pure could participate in such a feast.
18 Consider the people of Israel: are not those who eat the sacrifices participants in the altar?