Written by Ambrose, Bishop of Milan, at the request of Gratian, the Emperor of the West as a counter to the influence of Arianism which at that time (A.D. 378) was growing rapidly. The object was to prove the divinity of Jesus, His co-eternity, co-equality and consubstantiality as God the Son with God the Father. He constantly appeals to the Old and New Testament Scriptures, which the Arians had in many cases forced into a false interpretation to make them fit their doctrine.
Along with St. Gregory the Great, St. Jerome, and St. Augustine, St. Ambrose is considered one of the original Doctors of the Church. He played an important role in the conversion of St. Augustine.