This is actually a one-sentence salutation including the usual elements of a letter: the writer's name and names of his companions, the intended readers, and a note of divine authority. As most commentators have observed, Paul generally included as well a prayer on behalf of his readers and a commendation for their witness. This salutation is different in that respect, and in omitting the commendation, it seems to reflect Paul's disturbance at the word he has received concerning the churches of Galatia.
To prepare for a strong defense of his own preaching, the opening paragraph includes a clear affirmation of Paul's commission as an apostle from Jesus Christ and from God the Father. Perhaps the readers had been told that Paul's apostolic claim lacked authenticity since it did not come from the original apostles in Jerusalem. Paul implies, however, that he holds ministerial equality with the Twelve, as he too was commissioned by God just as they had been commissioned by Christ (Burton, 363).
The salutation closes with a doxology of praise to God whose redemptive plan was revealed in Jesus Christ. It is the only epistle with such a designation of Christ in the introduction. This may indicate, as the Wesleyan Bible Commentary suggests, that the Galatians had “ignored the atoning death of Jesus in their emphasis on fulfillment through works” (p. 386).