"De Fide"
(On the Christian Faith)
by Ambrose of Milan

Ambrose of Milan set out to write the treatise entitled De Fide (On Christian Faith) upon the request from Emperor Gratian, who asked him to write a treatise on the proof of Jesus Christ’s Divinity. Gratian wanted Ambrose to formulate an argument against Arianism, which had, at that time, gained the upper hand over Church Orthodoxy in the East. Emperor Gratian was so pleased with Ambrose’s treatise that he begged Ambrose to expand on it by arguing for the Divinity of the Holy Spirit as well.  Ambrose did expand on it, but rather than dealing with the Divinity of the Holy Spirit, it instead addressed new objections that had been raised by the Arian Heresy.  Ambrose did so by constant appeal to the Scriptures, both of the Old and of the New Testament, which the Arian Heretics had in many cases twisted with false interpretation to make the Scriptures fit their false doctrine. 

Source Used:  Nicene and Post-Nicene Fathers, Second SeriesVol. 10.  Translated by H. de Romestin, E. de Romestin and H.T.F. Duckworth.Edited by Philip Schaff and Henry Wace.