How could Paul judge the immoral man in Corinth if he was not physically present?
Paul could judge the immoral man because though absent in body, he was present in spirit, and he pronounced judgment in the name of the Lord Jesus Christ, with the power of the Lord Jesus Christ present when the church gathered together.
Les explains that Paul told the Corinthians he was absent in body but present in spirit, and he had already judged the one who committed this deed as though he were present. The judgment was to be carried out in the name of the Lord Jesus Christ, when they gathered together with Paul's spirit and the power of the Lord Jesus Christ, delivering the man to Satan for the destruction of the flesh, not the soul—physical death if he would not straighten up. Les also notes that the second letter shows they dealt with it, brought the man back into fellowship, and his sin was forgiven and cleansed; the letter had done its work.
For I verily, as absent in body, but present in spirit, have judged already, as though I were present, concerning him that hath so done this deed,
More Questions
What did Paul mean by delivering the immoral man to Satan for the destruction of the flesh?
Paul, though absent in body but present in spirit, had already judged the offender, so that when gathered together in the name and power of the Lord Jesus Christ, such a one would be delivered unto Satan for the destruction of the flesh — not the soul — meaning physical death if the man would not straighten up.
What did Paul mean when he said he was absent in body but present in spirit?
Paul, though absent in body, was present in spirit and has already judged and reached a conclusion about the man who committed the deed.