1 Corinthians 10:21

It is inconsistent for a Christian to partake in the Lord’s Supper and to take part in pagan religious feasts. In the former he eats and drinks in union with Christ, and in the latter he is in union with demons who direct the devotees to worship idols. What the Lord promotes and what the demons promote are opposite. This inconsistency must be obvious to "wise men" (1 Corinthians 10:15). Christians have a unique relationship with the Lord and with fellow believers, which the Lord’s Supper symbolizes. It is, therefore, inappropriate for us to have a similar association with demons and unbelievers (1 Corinthians 10:20-21), which participation in pagan cultic events involves.