Faustus, first abbot of the monastery at Lerins, and then made bishop of Riez in Gaul, a man studious of the Divine Scriptures, taking his text from the historic creed of the church, composed a book On the Holy Spirit, in which he shows from the belief of the fathers, that the Holy Spirit is consubstantial and coeternal with the Father and the Son, the fullness of the Trinity and therefore God. He published also an excellent work, On the grace of God, through which we are saved, in which he teaches that the grace of God always invites, precedes and helps our will, and whatever gain that freedom of will may attain for its pious effect, is not its own desert, but the gift of grace. I have read also a little book of his Against the Arians and Macedonians, in which he posits a coëssential Trinity, and another against those who say that there is anything incorporeal in created things, in which he maintains from the testimony of Scriptures, and by quotations from the fathers, that nothing is to be regarded as incorporeal but God. There is also a letter of his, written in the form of a little book, and addressed to a certain deacon, named Graecus, who, leaving the Catholic faith, had gone over to the Nestorian impiety.
In this epistle he admonishes him to believe that the holy Virgin Mary did not bring forth a mere human being, who afterwards should receive divinity, but true God in true man. There are still other works by him, but as I have not read, I do not care to mention them. This excellent doctor is enthusiastically believed in and admired. He wrote afterwards also to Felix, the Prætonian prefect, and a man of Patrician rank, son of Magnus the consul, a very pious letter, exhorting to the fear of God, a work well fitted to induce one to repent with his whole heart.
Source: Illustrious Men (Supplement to Jerome) (New Advent)