Here again he hints that strife and party-spirit, love of rule and presumptousness, had been the causes of their error, for the desire of rule is the mother of heresies. By saying, "Be servants one to another," he shows that the evil had arisen from this presumptuous and arrogant spirit, and therefore he applies a corresponding remedy. As your divisions arose from your desire to domineer over each other, "serve one another;" thus will ye be reconciled again. However, he does not openly express their fault, but he openly tells them its corrective, that through this they may become aware of that; as if one were not to tell an immodest person of his immodesty, but were continually to exhort him to chastity. He that loves his neighbor as he ought, declines not to be servant to him more humbly than any servant. As fire, brought into contact with wax, easily softens it, so does the warmth of love dissolve all arrogance and presumption more powerfully than fire. Wherefore he says not, "love one another," merely, but, "be servants one to another," thus signifying the intensity of the affection. When the yoke of the Law was taken off them that they might not caper off and away another was laid on, that of love, stronger than the former, yet far lighter and pleasanter.
John Chrysostom, Commentary on the Epistle to the Galatians
(HT: Wilson in the comments at verbum ipsum)