“The mention of the Holy Spirit here is significant for several reasons. First, the grammatical form of the statement, rather than asserting that human judgment is the same as divine, is a Greek (and possibly Semitic) way of indicating a decree. Thus, what is to follow is meant to have binding force. Secondly, the decree has this force on the basis of the work of the Holy Spirit. This seems to be a recognition on the part of the church that the Spirit was involved in this last decision, in the same way that it had been involved in previous events in the development of the Church (cf. Acts 5:3, 9; 13:2), including the incorporation of the Gentiles (15:8, 12). Thirdly, as Johnson [L. T. Johnson, Acts, 277] points out, ‘The invocation of the Holy Spirit as a partner to the decision has an odd sound to contemporary ears, but it nicely captures the dynamics of the process as portrayed by Luke,’ including the role played by the Spirit and humans in Acts 13:1–3. Fourthly, there is no specification regarding how it is that James or others had it communicated to them or knew that it was good to the Holy Spirit to act in the way specified.”
Stanley E. Porter, Paul in Acts, Library of Pauline Studies, ed. Stanley E. Porter (Peabody, MA: Hendrickson, 2001), 76–7.