He was ordained a priest of that church in 381 and participated in the small Synod of Aquileia organized by Ambrose of Milan.

He was one of the most celebrated prelates of his time and was in active correspondence with contemporaries Ambrose, Jerome, and Tyrannius Rufinus.

[2] As a scholarly theologian, he urged these friends to produce learned works.

Ambrose was encouraged by him to write exegetical works; Jerome dedicated to him translations and commentaries, which he had written at his suggestion (translations of the Books of Paralipomenon, Tobit, the books of Solomon, commentaries on the Prophecy of Habakkuk).

He gave steadfast support to John Chrysostom, Archbishop of Constantinople, when he was unjustly oppressed, and wrote in his favour to Honorius, the Western emperor, who sent this letter to his brother, Arcadius.