Some disciples in Corinth were claiming, “I am of Paul” (1 Cor. 1:12). One essential condition of making such a claim was that such persons must have been “baptized in the name of Paul” (1:13). Since they were not “baptized in the name of 
Paul,” they could not be “of Paul”!
Some today are claiming, “I am of Christ” (i.e., I am a Christian, a follower of Christ). But are they truly? An essential condition for making such a claim is that such persons must have been “baptized in the name of Christ.” (Such is the force of Paul’s statement in verse 13.) But, to be baptized “in the name of Christ” requires that one is baptized “for [i.e., in order to obtain] the forgiveness of sins” (Acts 2:38). If one has been baptized for some other purpose other than obtaining forgiveness of sins, then such a person has not been baptized in the name of Christ, and thus such a person cannot claim to be “of Christ.” That is not some manmade doctrine, but is the only conclusion consistent with First Corinthians 1:12-13 and Acts 2:38.