Famous Orthodox Hymn in Galatians?

Dr. Constantinou continues her discussion of Galatians and some of its most famous passages. Galatians is the source of one of the most famous Orthodox hymns. St. Paul wrote the verses which became our baptismal hymn, and then he stated that there is neither male or female, slave nor free, Jew nor Greek. How did the Fathers of the Church explain that important passage?