The largest of these Jesus Only churches is the United Pentecostal Church, and in all about 25% of Pentecostals in the USA are unitarian or deny the Trinity. Other denominations include The Bible Way Churches of Our Lord Jesus Christ; The Church of Jesus Christ’ Apostolic Overcoming Holy Church of God, Inc.; Assemblies of the Lord Jesus Christ; Pentecostal Assemblies of God’ Assemblies of the Lord Jesus Christ’ Pentecostal Assemblies of The World; and the Church of the Lord Jesus Christ of the Apostolic Faith.
They often teach the Trinity is a belief in 3 Gods or that it is a doctrine created by the Roman Catholic Church. But the Trinity is not about 3 Gods and the teaching of the Trinity was clearly present well before the existence of the Catholic Church.
If God is unitarian, then Islam, Jehovah’s Witnesses, Christadelphians, and other unitarian groups are right and Christianity is wrong. Biblically, however, the only true God is Trinitarian” One God who exists in three Persons and one substance.
If there is no Trinity, there would be no incarnation, no objective redemption and therefore no salvation; for there would be no one capable of acting as Mediator between man and God.
When Jesus declared that “there is another who bears witness of Me” (John 5:32), this must mean that Jesus is not the Father. The Bible declares that the Father sent the Son and that the Son sent the Holy Spirit, we must be dealing with distinct Persons. For one person to send another person requires two persons, not one person.
If Jesus alone is God, and the Spirit, Son and Father His sequential modes, and they cannot co-exist, how is Jesus baptized and simultaneously the Spirit descends as a dove and the Father declares, “this is MY beloved Son, in whom I am well-pleased” (Matthew 3:17)?
Other scriptures where the Persons of the Godhead is often seen simultaneously, and they often interact with one another: Genesis 1:26; 3:22;11:7; Psalm 2:7; 104:30; 110:1; Matthew 28:19; John 14:16).
Like most cults, the United Pentecostal Church believes they are restoring biblical doctrine and biblical teaching that had been lost because of the supposed corruption of the church throughout the centuries. The fact is all they are doing is reviving the ancient heresy of modalism that has been rejected by the Church.
Quotes from early Christian writers affirming distinct Persons of the one God who coexisted eternally before the Roman Catholic Church:
140 AD Aristides “[Christians] are they who, above every people of the Earth, have found the truth, for they acknowledge God, the creator and maker of all things, in the only-begotten Son and in the Holy Spirit” (Apology 16).
150 AD Justin Martyr “God speaks in the creation of man with the very same design, in the following words: ‘Let us make man after our image and likeness’ . . . I shall quote again the words narrated by Moses himself, from which we can indisputably learn that [God] conversed with someone numerically distinct from himself and also a rational being. . . . But this Offspring who was truly brought forth from the Father, was with the Father before all the creatures, and the Father communed with him” (Dialogue with Trypho the Jew 62).
150 AD Polycarp of Smyrna “I praise you for all things, I bless you, I glorify you, along with the everlasting and heavenly Jesus Christ, your beloved Son, with whom, to you and the Holy Spirit, be glory both now and to all coming ages. Amen” (Martyrdom of Polycarp 14).
180 AD Irenaeus “But the Son, eternally co-existing with the Father, from of old, yea, from the beginning, always reveals the Father to Angels, Archangels, Powers, Virtues…” (Against Heresies, Book II, ch. 30, section 9)
180 AD Irenaeus “It was not angels, therefore, who made us, nor who formed us, neither had angels power to make an image of God, nor any one else, except the Word of the Lord, nor any Power remotely distant from the Father of all things. For God did not stand in need of these [beings], in order to the accomplishing of what He had Himself determined with Himself beforehand should be done, as if He did not possess His own hands. For with Him were always present the Word and Wisdom, the Son and the Spirit, by whom and in whom, freely and spontaneously, He made all things, to whom also He speaks, saying, “Let Us make man after Our image and likeness; ” [Gen. 1:26]” (Against Heresies 4:20:1).
190 AD Clement Of Alexandria “I understand nothing else than the Holy Trinity to be meant; for the third is the Holy Spirit, and the Son is the second, by whom all things were made according to the will of the Father.” (Stromata, Book V, ch. 14)
190 AD Clement Of Alexandria “When [John] says: ‘What was from the beginning [1 John 1:1],’ he touches upon the generation without beginning of the Son, who is co-equal with the Father. ‘Was,’ therefore, is indicative of an eternity without a beginning, just as the Word Himself, that is the Son, being one with the Father in regard to equality of substance, is eternal and uncreated. That the word always existed is signified by the saying: ‘In the beginning was the Word’ [John 1:1].” (fragment in Eusebius History, Bk 6 Ch 14; Jurgens, p. 188)
200 AD Tertullian “All the Scriptures give clear proof of the Trinity, and it is from these that our principle is deduced…the distinction of the Trinity is quite clearly displayed.” (Against Praxeas, ch 11)
200 AD Tertullian “Thus the connection of the Father in the Son, and of the Son in the Paraclete, produces three coherent Persons, who are yet distinct One from Another. These Three are, one essence, not one Person, as it is said, ‘I and my Father are One’ [John 10:30], in respect of unity of Being not singularity of number” (Against Praxeas, 25)
225 AD Origen “Nothing in the Trinity can be called greater or less, since the fountain of divinity alone contains all things by His word and reason, and by the Spirit of His mouth sanctifies all things which are worthy of sanctification.” (De Principis, Book I, ch. 3, section 7)
Reference: Encyclopedia of Cults and New Religions