The Trinity is a theological concept that makes the claim that the Christian God is three distinct persons--Father, Son, and Holy Spirit--yet is entirely whole or one. This is a doctrine that arises out of the reconciling of various passages of Scripture, some claiming that God is one, and many claiming each the Father, Son (Jesus), and the Holy Spirit are God. It arose in earliest Christianity and was affirmed by the earliest Ecumenical Church Councils.
The concept of the Trinity in conventional Christianity is as set out in the Nicene Creed, that Christ is "begotten, not made, being of one substance with the Father" , that God (the Creator and Father), the Son, (Jesus the Christ) and the Holy Spirit are one Essence or substance (in Greek, homoousios) and Three Persons (in Greek, hypostasis). This is accepted doctrine in the Eastern Orthodox Church, the Roman Catholic Church and nearly all Protestant denominations. There are, however, some differences of interpretation, (see Filoque).
The question of the Trinity and the closely related question of the nature of Christ were hotly debated from about the third to fifth century. Several alternate interpretations were supported by some bishops, but condemned as heresies:
In the 6th-11th century, the "Filioque" controversy arose between the Eastern and Western church over the issue of the origination of the Holy Spirit. While neither group argued that the Holy Spirit himself was created, there was disagreement as to whether he emanated from the Father and Son together or the Father alone.
The controversy was in regards to the Nicene Creed established in 325 A.D. and revised in 381 A.D. It states, "And [I believe] in the Holy Ghost, the Lord and Giver of life, who proceedeth from the Father." During a local council in Toledo, the phrase "and the Son" (Filioque in Latin) was added to the end of this section. This was based on the idea that the Father and Son are united in essence, so the Holy Spirit should proceed from them both rather than just the former.
Many members of the church, especially in the East, were concerned with this change as it seemed to contradict a statement in the Gospel of John 15:26, "But when the Helper comes, whom I [Jesus] will send to you from the Father, the Spirit of truth, who proceeds from the Father, he will bear witness about me." (English Standard Version) This controversy was one of many that caused the Schism between the Eastern and Western church in 1054 A.D.