1 Corinthians 11:28

'But let a man prove himself, and so let him eat of the bread, and drink of the cup.'

So the warning comes that each one should test and prove himself, presumably by self-examination, by a coming to the blood of Christ for cleansing (1 John 1:7), and then by a deliberate act of unity in coming together as one with the whole church, before he partakes of the Lord's Supper. He is to examine his heart and ensure that there is nothing in his life which is at present displeasing to God. Then, once his heart is right, his conscience is clear, and he is at one with his brothers, he may eat of the bread and drink of the cup, in solemn reaffirmation of his faith and position in Christ.