Three Persons: One God
God is one
Both divine revelation (the Holy Scriptures) and reason (in subjection to Scripture) can be appealed to as evidence to establish the truth of the oneness of God.
In contrast to the perversions of pagan religions, divine Revelation is rich in presenting only one true and living God (Deuteronomy 6:4; 4:35; Isaiah 43:10-11; 44:6; 45:5; Mark 10:18; 12:29; 1 Timothy 2:5).
And this same God is revealed to us by his attributes, works, names, and words. Reason thus collaborates with revelation, for if God is eternal, then any god that is not eternal is not God. If God is immense there is necessarily room for only one God ("Do I not fill heaven and earth?").
Again, there cannot be two or more omnipotent Gods. If there is more than one God then the allegiance of us creatures would be divided; we would not be able to love a number of gods with all our hearts and all of our souls and all of our minds: You cannot serve two Masters....
New Testament evidences
The unity of God is still presented in full force in the New Testament, no less than in the Old Testament. "Well, Master, thou hast said the truth: for there is one God; and there is none other but he" (Mark 12:32).
The Divine Name is numerically one, and yet in this One Name there are three persons distinguished: The Father, the Son and the Holy Spirit (Matthew 28:19-20).
The church receives her benediction from peculiar blessing for each of these Three (2 Corinthians 13:14).
Their different personalities are recognised (1 Corinthians 12:4-6). Christ refers to Himself with the pronoun "I," and at the same time to the Father as "He," and to the Spirit (who proceeds from the Father, and thus distinct from Him), again as "He," rather than "it," clearly meaning a person, not an influence or mere power. And yet these
Three possess the one indivisible divine essence, and are constituted distinct persons by certain incommunicable properties, not common in one with the other two.
They have distinct orders of operation, and consult and speak to each other. With reason then we worship "One God in trinity and trinity in unity; neither confounding the persons, nor separating the substance....And yet there are not three eternals, but one eternal.
The truth of the Trinity opposes the following errors:
This ancient heresy proposes a Modal Trinity, the One God having three aspects or manifestations of one person. Thus the Father could present himself as the Son, and in turn the Son could be manifested as the Spirit.
This is confounding the distinctness of the three persons, making the Father purely synonymous with the Son and the same as the Spirit.
The orthodox doctrine rejects this confusion, for while Christ is speaking on earth, he refers at the same time to the Father which is in heaven. Evidently He and the Father are not the same person.
This claims that the three persons are three essentials or elements of One God. Together they make one God: in the mathematical sense that one third plus one third plus one third make one whole. Or in the sense that body and soul and spirit constitute man.
This is erroneous for in each person of the Trinity the fullness of deity dwells (e.g. Colossians 2:9). Each of them does not have only a part of the divine essence.
Polytheism Polytheism maintains that there are many gods. But Scripture presents it as a foundational truth of all godliness this confession: "Hear O Israel: the Lord thy God is one Lord." "For us there is only one God."
Though incomprehensible to finite minds, the eternal subsistence of the blessed Three in One Essence cannot be said to be an evolutionary idea.
Even in the earliest stages of God's self-revelation, we are taught by intimation and implication that in the One God there is more than one person. Elohim (plural form of God), instead of Eloah (singular) is regularly used of God with a verb in the singular.
The Hebrew word for compound unity (echad) is used instead of the one denoting absolute oneness (yacheed). In speaking, God, who is manifestly One, says, "We will make..." thus hinting at his own Tri-unity.
The Son is specifically said to be Deity in distinction from the Father and his theophanies further confirm him as distinguished from the Lord and yet identified with God. Direct statement, though sparse, show that the Old Testament does not emphasise the unity of God (in essence) to the exclusion of his Tri-unity (of persons) cf. Isaiah 48:16; 61:1-2.
Tritheism and its dangers
Hot controversy has generally raged within the church throughout the centuries over the sublime doctrine of the Trinity. Because of the ineffable nature of God, men have often stumbled by twisting Scripture testimony to suit their own limited understanding of God.
Among such were the Tritheists, such as John Ascusnages of Constantinople and John Philoponus of Alexandria (latter part of 6th century).
Tritheism attempts to solve the issue of the unity and Threeness of God by denying his unity and placing all the emphasis on the persons, to such an extent that the Father, the Son and the Holy Spirit are denominated as three distinct Gods. Tritheists maintain that there are three Substances numerically considered, as well as three persons, one for each Substance.
The danger of such a theological position is extreme, since in such a case one will be worshipping three distinct Gods, which the Bible condemns as idolatry and polytheism (many Gods), whilst the confession of the people of God was and continues to be, "Hear, O Israel, the Lord your God is one Lord...."
A Tritheist cannot be in possession of salvation, because Scripture declares that no idolater has any inheritance in the kingdom of Christ and of God. Though confessing Father, Son and Spirit, the tritheist does not confess the true and living God, for three distinct Gods is a totally foreign idea to Scripture.
As the Athanasian Creed concludes (in which is a full and perspicuous statement of the Trinity), "This is the Catholic faith, which, unless a man shall faithfully and firmly believe, he can not be saved."