Q . 108. What is required to the worthy receiving of the Lord’s Supper?
A. It is required of them that would worthily (that is, suitably) partake of the Lord’s Supper, that they examine themselves, of their knowledge to discern the Lord’s body; of their faith to feed upon Him; of their repentance, love, and new obedience: lest, coming unworthily, they eat and drink judgment to themselves.
Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty concerning the body and blood of the Lord. Let a person examine himself, then, and so eat of the bread and drink of the cup. For anyone who eats and drinks without discerning the body eats and drinks judgment on himself. That is why many of you are weak and ill, and some have died. But if we judged ourselves truly, we would not be judged.
1 Corinthians 11:27-31
Let us therefore celebrate the festival, not with the old leaven, the leaven of malice and evil, but with the unleavened bread of sincerity and truth.
1 Corinthians 5:8
Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you? —unless indeed you fail to meet the test!
2 Corinthians 13:5