This is a common misconception about what the Trinity doctrine says, which actually has the opposite intent – to preserve the biblical witness to the oneness of God’s Being, yet at the same time accounting for the divinity of the Father, Son and the Spirit. The answer is that we must not confuse tritheism with the Trinity or think of "persons" as we do in the human sphere when we speak of God’s divine nature. What the Trinity says is that God is one with respect to his essence but is three with respect to the internal distinctions within his Triunity.

Here is how Christian scholar Emery Bancroft described it in his book Christian Theology, pages 87-88:

When we are seeking to understand the Trinity doctrine, we need to be careful how we use and understand the word "God." For example, whatever the New Testament says about the oneness of God, it also draws a distinction between Jesus Christ and God the Father. This is where the above formula from Bancroft is helpful. To be precise, we should speak of "God the Father," "God the Son" and "God the Holy Spirit" when we are referring to each hypostasis or "Person" of the one God.

It is legitimate to speak about the limitations of using the word "person" when explaining the nature of God. Do we really understand how God can be one in Being and three in Person? We have no experiential knowledge of God as he is. Not only is our experience limited, but so is our language. Using the word "Persons" for each of the three hypostases of God is in some ways a compromise. That’s true. But, when speaking to God’s nature, we need a word that emphasizes his personalness in relationship to us human creatures and within himself, and yet, that carries with it the concept of distinctiveness. "Person" just happens to be the most appropriate word we have in the English language to do this.

Unfortunately, the word "person" also contains the notion of separateness when used of human persons. How can we deal with this? The thing to understand is that God does not consist of the kind of persons that a group of human beings do. But, then, what is a "God-kind" of person? We can say that human persons are separate from each other and have separate wills because they only have external relations with each other, while the Persons of God have internal relations and share the same essence.

The Trinity doctrine uses the word "Person" for each hypostasis of God because it is a personal word, and above all, God is a personal being in his dealings with us. Only a personal being can love, and love is the defining essence of God, according to the biblical witness (1 John 4:8; John 3:16; 15:9-10)

The word "persons" distinguishes between the three Persons of God and the one Being of God in the sense that the three Persons constitute his one Being. Thus, the doctrine preserves both the biblical revelation that there is but one God and no other, as well as its testimony that the Father, the Son and the Spirit are all equally divine and true God of true God.

Those who reject the Trinitarian explanation of God’s nature are in a quandary. If one rejects the theology of the Trinity, he or she has no explanation that preserves two witnesses to God’s Being: God is One Being and also he is Triune in his Being.

That is why Christians formulated the doctrine in precise technical language – so that we could rightly speak of God, according to the witness he has left us of himself through Christ and in the Spirit, as attested to by the New Testament. The Church confesses the biblical testimony that God is one divine Being. But Christians also confess that Jesus Christ and the Holy Spirit are divine, true God of true God, according to the New Testament.

The Trinity doctrine was developed precisely with the intent of explaining, as well as human words and thought would allow, the reality that God has existed from eternity both as One Being and yet as three Persons. The Trinity doctrine says that God is one and that in his oneness he is Triune.

Explanations of the nature of God other than the Trinity have been put forth throughout the history of the Church. Arianism is one example. This theory claimed that the Son was a created being. The Arians thought they had preserved the oneness of God in their explanation, but created a heresy that did not rightly speak of God’s nature. The Arian conclusion was fundamentally flawed in that if the Son was a created being, he would not be divine, of the same essence of God, and therefore, could not be our Savior. For it is only God who can save us in new creation, in his Incarnate life, death and resurrection. All other theories advanced to explain God’s nature in terms of the revelation of the Son and Holy Spirit have proved equally unfaithful to the gospel and the nature of God.

On the other hand, the Trinitarian explanation takes into consideration the divinity of the Father, the Son and Holy Spirit – and the biblical truth that there is only one God. That’s why the doctrine of the Trinity has survived for centuries as the explanation of God’s nature that preserves the truth of the biblical witness of who God is – and that he has saved us in himself through the Son and in the Spirit.