The brothers with Paul is likely a reference to fellow believers and/or teachers in Antioch (cf. Acts 13:1–2; Acts 14:26–28) who are with him as he writes the letter.1 Paul mentions these brothers in order to affirm that his understanding of the gospel is not unique (his own idea) but also shared by fellow believers.2
2 and all the brothers who are with me,To the churches of Galatia: