It is no secret that most of the Christendom do not spend much time looking at the Doctrine of the Trinity as a peculiar point of interest, nor do we spend much time trying to look at its implications and legitimacy. Any critic of this doctrine should note that historical Trinitarians are cautious in articulating their understanding of what they say about God, as it should be done with extreme caution and precision. The doctrine of the Trinity is a central tenet of Christian theology, emphasizing the oneness of God in three persons: the Father, the Son (Jesus Christ), and the Holy Spirit. The “One and Three” distinctions refer to the unity of God in essence and the diversity of persons within the Godhead.
Oneness (One) asserts the absolute oneness of God’s essence. Only one divine nature is shared ultimately and undividedly by the Father, the Son, and the Holy Spirit. Threeness (Three) mediates that while God is one in essence, the doctrine acknowledges the existence of three distinct persons within the Godhead. The Father, the Son, and the Holy Spirit are not interchangeable; they are distinct persons with unique roles in the divine plan. If we can expand further on the “One and Three” distinctions in the doctrine of the Trinity, we find the following.
- The oneness of God’s essence is often expressed using theological terminology such as “consubstantial” or “of the same substance.” This emphasizes that the Father, Son and Holy Spirit share a common and indivisible divine essence.
- The doctrine emphasizes monotheism, asserting that there is only one true God. This aligns with foundational Christian beliefs as expressed in passages like the Shema in the Old Testament (Deuteronomy 6:4), which declares the oneness of God.
- The distinct persons within the Trinity are not separate gods but are co-equal and co-eternal. Each person of the Trinity participates fully in the divine nature and exists in perfect unity.
- The distinctions among the persons are relational rather than essential. The Father begets the Son, and the Spirit proceeds from the Father (and the Son, according to the Filioque clause in Western Christianity).
- The New Testament provides glimpses of this Trinitarian relationship, such as Jesus’ baptism, where the Father speaks from heaven, the Son is baptized, and the Spirit descends like a dove (Matthew 3:16-17).
Historically, Christians articulated the essence of this doctrine precisely in creedal form and tried to lay bare what could be believed from a human linguistic construct. So, it is not unfair to look at, for instance, one of the earliest Christian Creeds to derive some understanding of the topic. In one of the earlier Creeds called the “Quicumque Vult,” or Athanasian Creed, Line 4, we discover what Christians are trying to say when elaborating this doctrine as it reads:
“the Catholic Faith is this, that we worship one God in Trinity and Trinity in Unity. Neither confounding the Persons, nor dividing the Substance. For there is one Person of the Father, another of the Son, and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost is all One, the Glory Equal, the Majesty Co-Eternal.”
A lot of criticism seems to be leveled at tritheism or the suspicion of three Gods, or it seems to point out that all these forms are simply one modality of God, which would then be modalism, but this is not what Christians say. We conceive the difficulty apparent when trying to articulate any thought about God. Still, when we nuance this biblical imperative, we identify and put together what God has revealed and spoken.
Not Three God’s but One God.
Usually, criticism against this doctrine implies that the Triunity of God implies divisibility. The question Christians are confronted with is if the idea of distinction contradicts what they say about God’s identity, and even more, does the concept of plurality contradict the essential unity of God? When Christians consider what God has revealed about Himself in the Biblical Scriptures, it should be noted that they hold to the fact that God is indivisible. This means that any divisible object can be divided without destroying the essence of that object itself. Look, for example, a stone. A block of stone can be split into two parts without damaging the stone as a stone. Now, it should be noted that I am not using indivisibility as an argument to describe the plurality of persons but instead to show that any assumed substance of the person of God stays in perfect harmony because any sharing of that substance cannot violate or break what the given object subsists off. William Henry Temple Gairdner comments:
“A hand when severed from the body is really not a hand at all. It is only a lump of flesh shaped like a hand; for it is of the essence of a hand to be one with the whole body, to communicate through its nerves with the brain, to share the one life of the whole. It is only by an abstraction, which contains as much falsehood as truth, that you say that the hand is a part of the body at all, if by that you mean that it exists as a hand after being severed from the body. It is only by a very partial abstraction you can do this, namely, by arbitrarily selecting some features which inhere in ‘hand’ and arbitrarily overlooking other equally or more important ones. 
You can divide the material of an organism, but you cannot divide the essence or nature of an organism. William Henry Temple Gairdner, therefore, speaks of God and says:
“God has no material substance. Therefore, He is, in every sense, both ideally and indivisible. An earthly organism, then, can only exist in the fulness of its nature or be destroyed—there is no third possibility such as division. God cannot be destroyed; therefore, He exists only in the undivided and indivisible fulness of His nature—that is, in His Unity of Father, Son, and Holy Spirit.” 
Does such a formulation make sense at all?
I find very often that Muslims attribute definitions to the Christian understanding of the Trinity that seem to violate the overall knowledge of the doctrine. Roger Nicole rightly emphasizes the proper balancing of three aspects of the Trinity in the chapter “The Meaning of the Trinity”, on the One God and Trinity Book edited by Peter Toon and James D. Spiceland. They show pretty clearly:
- If we overemphasize threeness, this leads to polytheism or tri-theism.
- If we overstress oneness, this leads us to modalism in which only one person is manifested as Father or Son or Spirit.
- If we reject equality, this leads to subordinationism (e.g., such as the Jehovah’s Witnesses’ distinction between Jehovah God and Jesus as “a god”).
In orthodox Christianity, (1) only one God exists; (2) this God exists eternally in three distinct persons (Father, Son, Spirit); (3) these persons are fully equal in every divine perfection; they possess alike the fullness of the divine essence. If you assume Tritheism, you will always wind up in a pickle with what you conceive the Trinity to be. I love how Gregory Nazianzus preached in the sermons at Constantinople on the 6th of January, 381 A.D. He beautifully says:
“No sooner do I conceive of the One than I am illumined by the Splendour of the Three; no sooner do I distinguish Them than I am carried back to the One. When I think of any One of the Three, I think of Him as the Whole, and my eyes are filled, and the greater part of what I am thinking of escapes me. I cannot grasp the greatness of That One so as to attribute a greater greatness to the Rest. When I contemplate the Three together, I see but one torch, and cannot divide or measure out the Undivided Light”.
Understanding this concept can be challenging, as it transcends human understanding. The Trinity’s unity and diversity underscore the divine nature’s complexity. We must recognize that we will always be novices when contemplating God. Articulating our understanding of God helps us define our beliefs and clarifies our expressions, even though our initial conceptions may necessitate rethinking and reshaping our articulation.
 New Advent, “The Athanasian Creed.” “Quicumque Vult” Line 4.
 God as Triune, Pg. 18.
 God as Triune, Pg. 18-19.
 Westchester, 111.: Cornerstone, 1980, Pg. 1-4.
 Gregory of Nazianzus, Orations 40.41. Source. Translated by Charles Gordon Browne and James Edward Swallow. From Nicene and Post-Nicene Fathers, Second Series, Vol. 7. Edited by Philip Schaff and Henry Wace.