God is a trinity of persons: the Father, the Son, and the Holy Spirit. The Father is not the same person as the Son; the Son is not the same person as the Holy Spirit; and the Holy Spirit is not the same person as Father. They are distinct persons; yet, they are all the one God. They are in absolute perfect harmony consisting of one substance. They are coeternal, coequal, and copowerful. If any one of the three were removed, there would be no God.
A further point of clarification is that God is not one person, the Father, with Jesus as a creation and the Holy Spirit as a force. Neither is He one person who took three consecutive forms, i.e., the Father, became the Son, who became the Holy Spirit. Nor is He one person who has 3 separate identities, i.e. He is called "Father" in some instance, "Son" in another, and "Holy Spirit" in another; much like a man is a "Father", to his children, and a "Son" to his parents, and a "soul mate" to his wife. Nor is God the divine nature of the Son; where Jesus had a human nature "perceived as the Son and a divine nature "perceived" as the Father, with the Holy Spirit as the name of the "power force". Lastly the "Trinity" , is not an "office" held by three separate Gods.
Father, Son and Holy Spirit are three persons who are one. They are like the clover. It has 3 distinct petals, yet it is one leaf. They are like an egg. The egg has 3 distinct parts, the shell, the yolk, and the white. They have different compositions, they can separate, yet they are all the egg. One could even describe the Trinity as being like the Bible that you hold in your hand. It is made with ink, paper and the cover, yet it is one Book.
The chart below should help you to see how the doctrine of the Trinity is derived from Scripture. The list is not exhaustive, only illustrative. "I am the LORD, and there is no other; besides Me there is no God" (Isaiah 45:5).
Trinity
FATHER SON HOLY SPIRIT
Called God Phil. 1:2 John 1:1,14; Acts 5:3-4
Col.2:9
Creator Is. 64:8; John 1:3; Job 33:4,26:13
44:24 Col. 1:15-17
Indwells 2 Cor. 6:16 Col. 1:27 John 14:17
Everywhere 1 Kings 8:27 Matt. 28:20 Ps. 139:7-10
All knowing 1 John 3:20 John 16:30; 1 Cor. 2:10-11
21:17
Sanctifies 1 Thess. 5:23 Heb. 2:11 1 Pet. 1:2
Life giver Gen. 2:7 John 1:3;5:21 2 Cor. 3:6,8
Fellowship 1 John 1:3 1Cor. 1:9 2 Cor. 13:14
Eternal Ps. 90:2 Micah 5:1-2 Rom. 8:11
A Will Luke 22:42 Luke 22:42 1 Cor. 12:11
Speaks Matt. 3:17 Luke 5:20;7:48 Acts 8:29; 11:12;
13:2
Love John 3:16 Eph. 5: 25 Rom. 15:30
The teaching that there are three "offices" in the godhead; is a doctrine of man, originating in the third century, with a Libyan priest named "Sabellius".
Of course, people immediately recognized that Sabellius's teaching contradicted the historic faith of the Church, and he was quickly excommunicated. His heresy became known as Sabellianism, Modalism, and Patripassianism. It was called Sabellianism after its founder, Modalism after the three modes or offices which it claimed the one Person of the Trinity occupied, and Patripassianism after its claim that the Person of the Father (Patri-) suffered (-passion) on the cross when Jesus died.
Because Modalism asserts that there is only one Person in the Godhead, it makes nonsense of passages which show Jesus talking to his Father (e.g., John 17), or declaring he is going to be with the Father (John 14:12, 28, 16:10, 17:5; one office of a Person cannot go to be with another office of that Person), or say that the two of them will send the Holy Spirit while they remain in heaven (John 14:17, 26, 15:26, 16:13-15; Acts 2:32-33).
Modalism quickly died out; it was too contrary to the ancient Christian faith to survive for long. Unfortunately, it was reintroduced in the nineteenth century in the American Holiness movement and subsequently passed into the Pentecostal movement when that started in the early twentieth century.
In its new form, Modalism is often referred to as "Jesus Only" theology since it claims that Jesus is the only Person in the Godhead and that the Father, the Son, and the Holy Spirit are merely names, modes, or offices of Jesus.
Today the United Pentecostal Church, as well as numerous smaller groups which call themselves "Apostolic churches," teach the Jesus Only doctrine. Through the Word Faith Movement, it has even begun to infect traditionally Trinitarian Pentecostalism. Ironically, Trinity Broadcasting Network, operated by Word Faith preacher Paul Crouch, has given a television voice to many of these Jesus Only preachers (who are, of course, anti-Trinitarian). Arnold Murray often mocks the practices of these television pastors, yet he too teaches the heresy of Modalism.
In the quotes that follow, one can see the forceful rejection of Modalism shown by the early Church fathers, and early martyrs.
The Letter of Barnabas
"And further, my brethren, if the Lord [Jesus] endured to suffer for our soul, he being the Lord of all the world, to whom God said at the foundation of the world, 'Let us make man after our image, and after our likeness,' understand how it was that he endured to suffer at the hand of men" (Letter of Barnabas 5 [A.D. 74]).
Hermas
"The Son of God is older than all his creation, so that he became the Father's adviser in his creation. Therefore also he is ancient" (The Shepherd 12 [A.D. 80]).
Ignatius of Antioch
"Jesus Christ . . . was with the Father before the beginning of time, and in the end was revealed. . . . Jesus Christ . . . came forth from one Father and is with and has gone to one [Father]. . .. [T]here is one God, who has manifested himself by Jesus Christ his Son, who is his eternal Word, not proceeding forth from silence, and who in all things pleased him that sent him" (Letter to the Magnesians 6-8 [A.D. 110]).
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 [A.D. 155]).
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 [A.D. 155]).
Mathetes
"[The Father] sent the Word that he might be manifested to the world . . . This is he who was from the beginning, who appeared as if new, and was found old . . . This is he who, being from everlasting, is today called the Son" (Letter to Diognetus 11 [A.D. 160]).
Irenaeus of Lyons
"It was not angels, therefore, who made us nor who formed us, neither had angels power to make an image of God, nor anyone else . . . For God did not stand in need of these 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 [the Father] 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 in our image and likeness' [Gen. 1:26" (Against Heresies 4:20:1 [A.D. 189]).
Tertullian
"While keeping to this demurrer always, there must, nevertheless, be place for reviewing for the sake of the instruction and protection of various persons. Otherwise it might seem that each perverse opinion is not examined but simply prejudged and condemned. This is especially so in the case of the present heresy [Sabellianism], which considers itself to have the pure truth when it supposes that one cannot believe in the one only God in any way other than by saying that Father, Son, and Spirit are the selfsame person. As if one were not all . . . through the unity of substance" (Against Praxeas 2:3-4 [A.D. 216]).
Tertullian
"Keep always in mind the rule of faith which I profess and by which I bear witness that the Father and the Son and the Spirit are inseparable from each other, and then you will understand what is meant by it. Observe, now, that I say the Father is other, and the Son is other, and the Spirit is other. . . . I say this, however, out of necessity, since they contend that the Father and the Son and the Spirit are the selfsame person" (ibid. 9:1 [A.D. 216]).
Hippolytus
"Thus, after the death of Zephyrinus, supposing that he had obtained (the position) after which he so eagerly pursued, he [Pope Callistus] excommunicated Sabellius, as not entertaining orthodox opinions" (Refutation of All Heresies 9:7 [A.D. 228]).
Novatian
"[W]ho does not acknowledge that the person of the Son is second after the Father, when he reads that it was said by the Father, consequently to the Son, 'Let us make man in our image and our likeness' [Gen. 1:26] . . . Or when he reads (as having been said) to Christ: 'Thou art my Son, this day have I begotten you. Ask of me, and I will give you the heathens for your inheritance, and the ends of the earth for your possession?' [Ps. 2:7-8]. Or when also that beloved writer says: 'The Lord said unto my Lord, Sit Thou on my right hand, until I shall make your enemies the stool of your feet?' [Ps. 110:1]. Or when, unfolding the prophecies of Isaiah, he finds it written thus: 'Thus says the Lord to Christ my Lord?' Or when he reads: 'I came not down from heaven to do mine own will, but the will of Him that sent me?' [John 6:28]. Or when he finds it written: 'Because He who sent me is greater than I?' [cf. John 14:24, 28]. . . . Or when he finds it placed side by side with others: 'Moreover, in your law it is written that the witness of two is true. I bear witness of myself, and the Father who sent me bears witness of me?' [cf. John 8:14-18]" (Treatise on the Trinity 26 [A.D. 235]).
Novatian
"And I should have enough to do were I to endeavor to gather together all the passages [of the kind in the previous quotation] . . . since the divine Scripture, not so much of the Old as also of the New Testament, everywhere shows Him to be born of the Father, by whom all things were made, and without whom nothing was made, who always has obeyed and obeys the Father; that He always has power over all things, but as delivered, as granted, as by the Father Himself permitted to Him. And what can be so evident proof that this is not the Father, but the Son; as that He is set forth as being obedient to God the Father, unless, if He be believed to be the Father, Christ may be said to be subjected to another God the Father?" (ibid.)
Gregory the Wonder-worker
"But some treat the Holy Trinity in an awful manner, when they confidently assert that there are not three persons, and introduce (the idea of) a person devoid of subsistence. Wherefore we clear ourselves of Sabellius, who says that the Father and the Son are the same [Person] . . . We forswear this, because we believe that three persons--namely, Father, Son, and Holy Spirit--are declared to possess the one Godhead: for the one divinity showing itself forth according to nature in the Trinity establishes the oneness of the nature" (A Sectional Confession of Faith 8 [A.D. 262]).
Gregory the Wonder-worker
"But if they say, 'How can there be three Persons, and how but one Divinity?' we shall make this reply: That there are indeed three persons, inasmuch as there is one person of God the Father, and one of the Lord the Son, and one of the Holy Spirit; and yet that there is but one divinity, inasmuch as . . . there is one substance in the Trinity" (ibid., 14).
Methodius
"For the kingdom of the Father, of the Son, and of the Holy Ghost, is one, even as their substance is one and their dominion one. Whence also, with one and the same adoration, we worship the one Deity in three Persons, subsisting without beginning, uncreated, without end, and to which there is no successor. For neither will the Father ever cease to be the Father, nor again the Son to be the Son and King, nor the Holy Ghost to be what in substance and personality He is. For nothing of the Trinity will suffer diminution, either in respect of eternity, or of communion, or of sovereignty" (Oration on the Psalms 5 [A.D. 305]).