1 Corinthians 11:26-28

For every time you eat this bread and drink this cup, you are [symbolically] proclaiming [the fact of] the Lord’s death until He comes [again]. So then whoever eats the bread or drinks the cup of the Lord in a way that is unworthy [of Him] will be guilty of [profaning and sinning against] the body and blood of the Lord. But a person must [prayerfully] examine himself [and his relationship to Christ], and only when he has done so should he eat of the bread and drink of the cup.