3.2.3 The development of the doctrine of the Trinity

The recognition of God's triune nature and its doctrinal presentation already began shortly after the New Testament Scriptures had been written. To express these interrelations linguistically, ancient philosophical terms like "person" or "hypostasis", as well as "substance", were used. Formulating the doctrine of the Trinity served, on one hand, to put into words the understanding gained through faith, and on the other, to protect the faith against heretics who sought to convey an image of God which did not correspond to the testimony of the New Testament. The doctrine of the Trinity was formulated during the first councils of the fourth and fifth centuries.


The term "Trinity" was coined by Theophile of Antioch, who lived in the second half of the second century, but it was the church leader Tertullian (ca. AD 160-220) who made it popular. Tertullian emphasised the oneness of God: "one [divine] substance in three persons" (Latin: una substantia tres personae). He was also the first to apply the term "person" to the Father, the Son, and the Holy Spirit.


The Council of Nicaea (AD 325) explicitly enshrined the divine oneness of substance of the Father and Son. The direct reason behind this was the doctrine of Arius (died AD 336), who argued that the pre-existent Son was created by the Father from nothing, which therefore constituted God's first act of creation. In opposition to this view, the council insisted that the Son was not created, but has been, from all eternity, part of the triune God.


This dispute, known as the "Arian controversy", did not come to an end with the Council of Nicaea, but went on until the Council of Constantinople in AD 381. This council brought to expression that the Holy Spirit is as much a divine person–and true God–as the Father and the Son.


In the following years, the doctrine of the Trinity was, with few exceptions, generally accepted by Christendom. The deliberations over the doctrine of the Trinity had, however, not been concluded. Particularly under the influence of the Church Father Augustine (AD 354-430), the Western Church later emphasised that the Holy Spirit emanates equally from both the Father and the Son. In contrast, the Eastern Church maintained an older version of the Creed of Nicaea-Constantinople, which states that the Holy Spirit emanates from the Father through the Son.


The Reformers adopted the belief in the Trinity of God from the early church (second to sixth century). With the exception of the aforementioned divergent interpretation concerning the Holy Spirit, the doctrine of the Trinity is common to all Christian churches. It is among the most fundamental statements of the Christian faith and is an essential feature that distinguishes it from the two other Abrahamic religions, Judaism and Islam.


At the eleventh church synod of Toledo (AD 675) it was proclaimed: "The Father is the same as the Son, the Son the same as the Father, the Father and the Son the same as the Holy Spirit, namely by nature one God."