The Apostle Paul places the whole Church of Ephesus with himself at the beginning of the epistle. By this he shows that it agrees with him in everything. In Ephesus there were beginnings of faith even before his arrival there (see Acts 18:21-24).
From this it followed directly that it was false to say that only he taught in this way. Rather, such is the spirit of Christianity: wherever it takes up its dwelling, there the synagogue must fall in its whole structure.
Thus Saint Chrysostom says: "Why does he not say this anywhere in the other epistles, but either sets down his own name alone, or names others, yet not more than two or three? Why here does he mention the whole multitude of the faithful, and why does he name no one? Why does he do this? The Judaizing Christians reproached him, saying that he alone preached in this way and thereby introduced a new teaching into the dogmas of the faith. Therefore, to destroy this suspicion and show that he has many who think as he does, he joins the brethren to himself. By this he shows that what he writes is in agreement with their thoughts also."
Others suppose that these words do not indicate the whole Church, but only those brethren who stood in a special relation to the Apostle. These included his fellow workers, and perhaps others besides them. As blessed Jerome observes, they were "known to the Galatians, honored by them, and themselves of the circumcision."
In the First Epistle to the Corinthians, written after the Epistle to the Galatians, Sosthenes is mentioned (see 1 Cor 1:1). In the Second, written after the First, Timothy is mentioned (see 2 Cor 1:1). Titus was sent to Corinth soon after the First Epistle there (see 2 Cor 2:13). All of them were evidently in Ephesus.
Aquila and Priscilla were there as well (see Acts 18:21). So too were Gaius and Aristarchus, Macedonians seized during the uprising against Saint Paul by the unbelieving Ephesians (see Acts 19:29). Perhaps some of the seven men mentioned as Saint Paul's companions on his return journey from Corinth were also there, about four months after his departure from Ephesus (see Acts 20:4).
All these were important persons, known throughout the circle of believers. Saint Paul may have meant them all, or the greater part of them, by the words, "all the brethren who are with me." He did not name them because they were many.
So says blessed Theodoret, who saw in these brethren those who assisted Saint Paul in preaching. Besides the reason given by Saint Chrysostom, the motive for Saint Paul's placing many beside himself may also have been, as Jerome writes, that "in correcting people, the agreement of many in one opinion has great weight."
For, according to Ambrosiaster, "one more easily understands his error when he sees that many are convicting him of it."
"To the Churches of Galatia." The Churches were not in one or two cities, but in many. Perhaps they were in all four of the best-known cities, and not only in them, but also in their surrounding districts. For this reason the epistle resembles a catholic or circular epistle.
Saint Chrysostom writes: "To the Churches of Galatia, because the flame of error had seized not one city, nor two or three, but the whole Galatian people. Notice here also the Apostle's great indignation. He did not say, 'to the beloved' or 'to the saints,' but simply, 'to the Churches of Galatia.' For this is the sign of one who is deeply grieved and in pain: he does not greet them by a name of love or honor, but only by the name of their society. He does not even add, 'to the Churches of God,' but simply says, 'to the Churches of Galatia.' Yet by this very name he hastens, at the very beginning, to recall their division to unity. For this reason he mentioned the name of the Church, to put them to shame and gather them into one. Since they were divided into many parts, they could not even be called by the name of the Church. For the name of the Church is a name of concord and unanimity."
THEOSIS