Adam Clarke on Acts 15:5

But there rose up certain of the sect of the Pharisees - This verse appears to be part of the declaration made by Paul and Barnabas to this council: for, having stated how God blessed their ministry among the Gentiles, they proceed to declare how all the good work was likely to be destroyed by certain Pharisees, who, having received the Christian faith, came down to Antioch, and began to teach the necessity of circumcision, etc., and thus filled the minds of the young converted Gentiles with doubtful disputations.