After the death of the Arian Emperor Valens, the synod of Antioch in 379 asked Gregory of Nazianzus to help resurrect Constantinople to the true Christian faith. While the most important churches were still headed by Arian bishops, Gregory transformed his cousin's villa into the Anastasia (Resurrection) chapel. From this little chapel he delivered five powerful discourses on Nicene doctrine, explaining the nature of the Trinity and the unity of the Godhead. These are called the "Theological Orations." By the time he left Constantinople two years later, there did not remain one Arian church in all of the city.
These orations have now been recorded for free download so that you can listen to them for yourself and benefit from the clear biblical thinking of this Cappadocian father -- every bit as relavant today as 1632 years ago.