Galatians 1:2

“And all the brethren which are with me, etc..] Meaning either the brethren of the church where he was when he wrote this epistle, who were children of the same Father, regenerated by the same grace, belonged to the same family and household of God, and were heirs together of the grace of life; or else his fellow ministers, who were assisting to him in his work, and were companions with him in his travels, and whom he sometimes mentions by name and joins with him in his epistles, as Sosthenes, Silvanus, and Timothy; and the rather he takes notice of the brethren here, whoever are meant, to show that they agreed with him in the doctrines of grace he defends, and in the charges he brought…”

“all the brethren--I am not alone in my doctrine; all my colleagues in the Gospel work, travelling with me (Act 19:29, Gaius and Aristarchus at Ephesus: Act 20:4, Sopater, Secundus, Timotheus, Tychicus, Trophimus, some, or all of these), join with me. Not that these were joint authors with Paul of the Epistle: but joined him in the sentiments and salutations. The phrase, "all the brethren," accords with a date when he had many travelling companions, he and they having to bear jointly the collection to Jerusalem [CONYBEARE and HOWSON]. the churches--Pessinus and Ancyra were the principal cities; but doubtless there were many other churches in Galatia (Act 18:23; Co1 16:1). He does not attach…”

“And all the brethren which are with me - It was usual for Paul to associate with him the ministers of the gospel, or other Christians who were with him, in expressing friendly salutations to the churches to which he wrote, or as uniting with him, and concurring in the sentiments which he expressed. Though Paul claimed to be inspired, yet it would do much to conciliate favor for what he advanced, if others also concurred with what he said, and especially if they were known to the churches to which the epistles were written. Sometimes the names of others were associated with his in the Epistle; see the 1 Corinthians 1:1 note; Philippians 1:1 note; Colossians 1:1 note; 1 Thessalonians 1:1 note.…”

“And all the brethren - Who agree with me in what I now write. Galatians 1:4”

“1:2 the brothers and sisters here join me: Paul probably wrote from Antioch of Syria. Antioch was the hub of Paul’s ministry and the earliest center of Gentile Christianity (see Acts 11:20-26). Paul did not stand alone (as his opponents in Galatia might have suggested), but in fellowship with a significant New Testament church. • The churches of Galatia were probably founded by Paul during his first missionary journey (Acts 13:4–14:26; see Galatians Book Introduction, “Recipients”).”

“all: Phi 2:22, Phi 4:21 churches: Act 9:31, Act 15:41, Act 16:5, Act 16:6, Act 18:23; Co1 16:1 Galatians 1:3”