The Lord’s Supper/Communion

In 1 Corinthians 11:17-30 Paul was talking about the Lord’s Supper; the unworthy manner of the Corinthians taking the Lord’s Supper. My questions are:
1. Why do almost all evangelical churches/pastors put emphasis on confession of sins before taking the Lord’s Supper? What are the biblical scriptures supporting this practice? In the passages (17-30) i cannot see the emphasis on confession. am i wrong in this interpretation?

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