Christianity holds that there is one God, but three persons—Father, Son, and Holy Spirit. This doctrine is known as the "Trinity." The doctrine has been a difficult one to understand, and was a topic of great dispute in the Early Church. Nevertheless, it is a central tenet of Christianity, and what separates Christianity from other monotheisms.
The doctrine reached a swelling point in the fourth century, when Arius claimed that Christ was created by God the Father, and was not co-eternal with him. Eventually, the Council of Nicene was convened to address Arius' claims. Led in part by St. Athanasius, it found Arius' claims heretical and formulated the Nicene Creed to discredit and correct them. For the next 100 years, Church Fathers would defend the doctrine of the Trinity from Arian challenges that still existed. Yet, by about the end of the fourth century, the doctrine of the Trinity took on, more or less, the form that we have today.
Although the Nicene Creed gave an initial formulation of the doctrine, Christian theologians and philosophers have not stopped discussing the doctrine. Gathered here is a list of what different Christians have said about the doctrine. Arranged chronologically, they show the doctrine developed and changed over time. The texts can be difficult at times, but are often thought-provoking.
CCEL Staff Writer
The result of the First Council of Nicene, the Nicene Creed states that the Son is of "one substance" with the Father, and not of a "similar" substance of the Father.
of the Nicene Definition by St. Athanasius (297-373)
In this work, St. Athanasius provides an account of the Arians at the Council of Nicene* and defends the Nicene Creed from criticism of it being unbiblical.'*
Third Theological Oration. On the Son. St. Gregory of Nazianzus (329-390)
In this oration, St. Gregory of Nazianzus defends the traditional, Nicene understanding of the Trinity, claiming that the persons of the Trinity are "numerically distinct" without a "severance of essence."*
Treatises by St. Gregory of Nyssa (335-394)
Although much controversy focused on the divinity of Christ, the doctrine of the Trinity also posits the Holy Spirit as divine. In this treatise, St. Gregory of Nyssa defends the divinity of the Holy Spirit through Scripture.*
on the Gospel of St. John by St. John Chrysostom (347-407)
In a homily on John 1, St. John Chrysostom argues that Scripture clearly teaches that God the Father and Christ are distinct, but not of a compound substance.*
the Holy Trinity by St. Augustine (354-430)
St. Augustine devoted an entire book to the topic of the Trinity. Among other things, he argues that the Trinity can be seen in Scripture,* responds to objections to the Trinity,* and demonstrates the equality of the Godhead.*
by St. Anselm (1033-1109)
St. Anselm seems to suggest that we lack any fitting language for describing the Trinity as "three," because terms like "person" or "substance" seem to only apply to things of plurality, of which God is not.*
on the Most Holy Trinity by St. Aquinas (1225-1274)
In a long treatise on the Trinity, St. Aquinas addresses many features of the Trinity including: the Divine relations,* knowledge of the Trinity,* the procession of the Trinity,* and the relationship of the members of the Trinity to God's essence.*
Declaration and Vindication of the Doctrine of the Trinity by John
Using both Scripture and reason, John Owen defends the doctrine of the Trinity against "Socinianism"—the view that Christ did not pre-exist before being a man.*
Theology, vol. 1 by Charles Hodge (1797-1878)
In a rigorous fashion, Hodge examines the Scriptural evidence for the Trinity,* the Nicene Creed,* and philosophical formulations of the doctrine.*
CCEL has other additional readings worth consulting:
Against the Arians by St. Athanasius (297-373)
An Exact Exposition of the Orthodox Faith by St. John of Damascus (675-749)
Of God and His Creatures by St. Thomas Aquinas (1225-1274)
Body of Divinity by Thomas Watson (1620-1686)
An Unpublished Essay on the Trinity by Jonathan Edwards (1703-1758)
Doctrinal Theology by Heinrich Schmid (1811-885)