1 Corinthians 10:21 (ESV)

21 You cannot drink the cup of the Lord and the cup of demons. You cannot partake of the table of the Lord and the table of demons.

God does not tolerate idolatry among his people (Exodus 20:3–5). Therefore, it is impossible to partake in his table and in the table of demons.

In this verse, Paul is clearly connecting the Lord’s Supper with the sacrificial feast of the Old Testament. It is a natural connection to make, since the Lord’s Supper was instituted during the sacrificial meal of Passover (Luke 22:7–20). As the Old Testament believers enjoyed fellowship with God through eating sacrificial meals in the temple courts, so New Testament believers enjoy fellowship with him at the table of the Lord’s Supper.

In 1 Corinthians 10:21–22, Lord may refer to Christ, but it may also refer to the Father, as the one who received Christ’s sacrifice. See also 1 Corinthians 10:26.