Christians who reject the Trinity number about 3 percent of all believers
Most churches treat the Trinity as settled since councils in 325 and 381. Yet roughly 3 percent of today's Christians, from Jehovah's Witnesses to Oneness Pentecostals, reject it. Their objections are far older than the doctrine's formal definition, and some once ruled whole kingdoms, as Arianism did among the Visigoths until 589.
The orthodox position holds that God is three coequal, coeternal persons sharing one essence. The Council of Nicaea in 325 affirmed the Son's full divinity and the Council of Constantinople in 381 the Spirit's, with Ephesus following in 431. Before that codification, rival views were already circulating. Adoptionism, from the second century, held that Jesus became divine at his baptism or resurrection, and the Ebionites kept Jewish law and saw Jesus as Messiah and supreme prophet but not God.
Arius, who died in 336, taught that the Son was the first thing the Father created, before all ages, and that the Father then made everything through him, supplying the plan while the Son did the work. His ideas dominated parts of the Roman world, reaching a peak at the Third Council of Sirmium in 357, whose confession declared that terms about shared or similar substance should not be discussed at all because scripture never used them.
A different challenge came from modalism. Sabellius, active around 215, argued that Father, Son and Spirit were roles played by one divine person at different moments: creator, redeemer and indwelling spirit. Tertullian mocked this as Patripassianism, the idea that the Father himself suffered on the cross. Ironically, the word homoousion that the Nicene creed later used against Arius had earlier been used by Sabellians. At the opposite extreme, the sixth-century Alexandrian John Philoponus treated the three persons as three separate natures and deities.
Such views resurfaced among the Cathars from the 11th to 13th centuries, in the Unitarian movement of the Reformation, during the Enlightenment and in some groups of the Second Great Awakening. Today the largest nontrinitarian bodies include The Church of Jesus Christ of Latter-day Saints, Iglesia ni Cristo and La Luz del Mundo. Some Trinitarians dispute whether such groups count as Christian at all, although Unitarian-leaning figures such as Bishop John Colenso served within the Church of England.
Source: Nontrinitarianism
