Trinity

In most branches of Christianity, the Trinity is an eternally-coexisting entity consisting of God (the Father), Jesus Christ (the Son), and the Holy Spirit. Sometimes called the "Triune Godhead," most Christians do not consider the Trinity to be a Pantheon, as you would find in many polytheistic religions, but as "three persons in one God." This allows Christians to claim that they follow a monotheistic religion, while in essence worshipping three gods. The composition and nature of the Trinity has been a major topic of disagreement and confusion among Christians since it was adopted at the Council of Nicea in 325 C.E.

Biblical support
The Trinity is never mentioned by that name in the Bible. While God, Jesus, and the Holy Spirit are all mentioned separately throughout the New Testament, there are only two passages that are used by apologists in an attempt to support Trinitarian doctrine. Each of these passage reveal errors in translation or meaning when examined.

1 John 5:7-8
, which scholars call the Johannine Comma, is translated as follows:

Most of verse 7 is not found in the oldest and best Greek manuscripts of the New Testament and has been dropped from many modern translations. Another translation based on the older Greek read "For there are three that testify: the Spirit, the water, and the blood—and these three are in agreement." (Holman Christian Standard Bible) Scholars believe the Johannine Comma to be a later addition to the New Testament, inserted to justify the doctrines of the orthodoxy.

John 1:1
is often cited as in support of the trinity as well:

In this passage, there is no definite article before the word theos (god) in the third part of the sentence. Coptic translators and Origen of Alexandria (both c.200) indicated their belief that John included a definite article before theos when referring to the creator god, and left it out when he was not. It is believed that in this context it means that Jesus is not one with God in person, but in essence. The translation of John 1:1c as "the Word was God", therefore, is a topic of scholarly debate, as it could justifiably be translated "the Word was a god" without the reference vaguely supporting the Trinity doctrine. This is the way that the Jehovah's Witnesses have translated the passage in the New World Translation.

Origen, however, noted that John was not consistent in his use of a definite article when writing about god. Whether John meant the creator God in certain passages was a topic of debate as early as the second century, as evidenced by Origen's exegesis and the Sahidic Coptic translation being markedly anti-Gnostic. So it could be argued that both translations are equally valid.

Neither view, of course, addresses the possibility that John may well have been influenced by Greek polytheism, not consulted the other Gospel writers to make sure the details of his writings matched theirs, written a passage or two supporting a trinity, and been a bit inconsistent because he was just making it all up.

John 10:30
is also used to support the view of trinitarian belief:

However, like John 1:1 there is an issue of the definite article. The NETBible translators note:


 * The phrase ἕν ἐσμεν ({en esmen) is a significant assertion with trinitarian implications. ἕν is neutral, not masculine, so the assertion is not that Jesus and the Father are one person, but one “thing.” Identity of the two persons is not what is asserted, but essential unity (unity of essence).

Another way of putting this is that in essence all humans are the same, but all humans are not one person. Although both God and Jesus may both be divine heavenly bodies, they are not the same trinitarian being. The interpretation that any of these passages assert that God and Jesus are part of the trinity is not conclusively shown.

Interpretations
There have been a wide variety of different interpretations of the nature of the Trinity over the centuries. Many of these groups were persecuted and some of the Crusades were actually fought in Europe against these groups.
 * Modalism is an early Christian view that suggests that the three entities are different forms of a single God, in much the same way that water has solid, liquid, and gaseous forms. While some churches retain a modalistic interpretation, orthodox Trinitarians consider it to be heresy.
 * Adoptionism posits that Jesus was a normal human who became divine, either at his baptism or his ascension.
 * Arianism was an early Christian doctrine which claimed that Jesus was created by God the Father, who later worked through Jesus to create the Holy Spirit, setting up a hierarchical godhead of separate entities. The Arian Controversy was a major reason for the Council of Nicea, which defined the Christian orthodoxy and effectively declared Arianism heretical.
 * Unitarians deny the Trinity altogether, believing that there is one God, and that Jesus was merely a human prophet or perhaps a supernatural entity in his own right, but was not God in the flesh. There was a Unitarian Church that merged with the Universalist Church some time ago to create the Unitarian Universalist Church.  This church in modern day focuses more on universalism and in this way tends to be very open to atheists and many atheists attend.  Other examples of unitarianism include the following:
 * The Mormons believe that God, Jesus, and the Holy Spirit are separate entities with separate bodies, united in single purpose; this view is criticized by the orthodoxy as being a form of Tritheism, or worship of three separate gods.
 * Jehovah's Witnesses see Jehovah as God, Jesus as an angel and the Holy Spirit as Jehovah's "active force" and not as an entity.