Problem: Paul writes about a believer that was kicked out of the church in Corinth. Who is he referring to?
Solution: Depending on your view of a lost letter in between 1 and 2 Corinthians (see comments on 2 Corinthians 2:4), you will have different views on this question. It is the view of this author that the man mentioned here is the same man who was removed from fellowship in 1 Corinthians 5. The Corinthian church was formerly licentious, permitting this man to sleep with his stepmother. However, after Paul’s rebuke in 1 Corinthians, they must have swung to the opposite side of the spectrum, taking an unforgiving stance in church discipline (c.f. 1 Cor. 5:1-13; 3 Jn. 10).
“But if any have caused grief, he hath not grieved me, but in part: that I may not overcharge you all. Sufficient to such a man is this punishment, which was inflicted of many. So that contrariwise ye ought rather to forgive him, and comfort him, lest perhaps such a one should be swallowed up with overmuch sorrow. Wherefore I beseech you that ye would confirm your love toward him. (2 Cor 2:5-8)”