Jesus Christ is the second Person of the Godhead, sent by the Father as Jesus Christ to be God revealed in the flesh for our salvation. Jesus was conceived by the Holy Spirit and born of the virgin Mary, fully God and fully human, two natures in one Person.
Though Jesus was a human being, he was simultaneously true God of true God. In short, Jesus is God. This seems to perplex some people who ask, how could Jesus be God when he did such things as pray to God? They are confused by the idea that God is "one in three and three in one," that is, that God is the Father, the Son, and the Holy Spirit. How can God be one and yet be three "persons"? This is the central question about God’s nature that Christians through the ages have tried to answer. It has led them to form a Trinitarian explanation of God’s Being.
It is understandable that someone might have difficulty grasping the explanation of the nature of God. Part of the reason why the doctrine of God’s nature can be difficult to understand is due to the Greek terminology used to explain it. The early Greek and Latin Christian theologians were the first to wrestle with the problem of how to rightly discuss the nature of the one God in terms of his threeness—as God the Father, Jesus the Son and the Holy Spirit.
They used words like the Latin persona to refer to the "Persons" that compose the Being of God. Theologians of the early centuries wrote mostly in the Greek language, understandable to people living in their time and culture. But most people today have not been trained in theological terminology or know the Greek language. A certain amount of "translation" and explanation is necessary to understand such statements as "Jesus is God." This is especially so since the theologians of the early church who crafted the Trinitarian creeds used common Greek terminology that was given a wholly new meaning when used of God.
The phrase, "One God who is three Persons—Father, Son, and Holy Spirit," is a common way of referring to the Trinity. However, the ordinary meaning of the word "persons," for example, which is normally included in English-language definitions of the Trinity, can cause people to wrongly think of God as existing in three separate Beings. Thus, the ordinary meaning of the word “persons” as understood when applied to humans is misleading when it is applied to God. It gives the impression that God’s threeness lies in his being three separate individuals. This is not biblical. There is only One God, not two Gods (bitheism) or many Gods (polytheism). The Father is omnipresent, the Son is omnipresent, and the Holy Spirit is omnipresent, and they cannot be "separate" from one another as three Gods. Therefore, to avoid such an error, "Persons" in the Godhead should not be thought of in the same way as human "persons" like you and I are.
To repeat, when most English-speaking people think of one God who is three "Persons," they may incorrectly visualize God as being three separate divine Beings. In other words, the terms “persons” and “beings” are usually thought of, in English, as meaning the same thing. That is misleading, however, when these words are applied to God. The Bible reveals that Father, Son, and Holy Spirit are the way the one true God of the Bible is, or the way God exists eternally. God would not be God if the Father, the Son or the Holy Spirit were “separate” from him, because he has eternally existed as a Triune Being.
Let’s look more closely at the specific question of how the statement "Jesus is God" should be understood. The doctrine of the Trinity doesn’t say that Jesus Christ (or the Son of God) and the Father are "one and the same." That is a common misconception. Jesus was not his own Father, as some mistakenly interpret the Trinitarian explanation of the oneness of the Godhead. The Father, the Son and the Holy Spirit are distinct, that is, they are not the same person —but neither are they separate beings. The Father is not the Son and the Son is not the Father. The Holy Spirit is not the Father or the Son. They all three exist in communion, sharing one essence with each other as the one Being who is God.
Whatever the New Testament says about the oneness of God, it also draws a distinction between Jesus Christ and God the Father. That is the reason why the New Testament generally refrains from calling Jesus in his earthly, Incarnate sojourn by the term "God." (To be precise about it, John 1:1 speaks of the Logos, not Jesus, as theos.)
Alister E. McGrath in Understanding the Trinity stresses the distinction that the New Testament makes between Jesus and the Father:
It is also clear that God is not identified with Jesus. Jesus refers to God as someone other than himself; he prays to God; and finally he commends his spirit to God as he dies. At no point does the New Testament even hint that the word "God" ceases to refer to the one who is in heaven, and refers solely to Jesus Christ during the period of his earthly existence [page 121].
Another scholar, John C. Dwyer, also points out this distinction in his book Son of Man and Son of God:
The word "God" in the New Testament means, almost without exception, "the One Jesus called ‘Father.’" This is by no means to assert that the New Testament takes no position on the question usually referred to as that of the divinity of Christ. But it is to assert that the statement "Jesus Christ is God" cannot be made as long as "God" is a word which refers to the one whom Jesus called "Father" [page 87].
When the New Testament and the Trinity define Jesus as "God" we should understand that they are not saying he is "his own father." In the New Testament, Jesus speaks and prays to the one called "Father," who is in heaven. The same distinction is made between the glorified Jesus and God the Father. For instance, in the book of Revelation it is clear that there is God, and there is Jesus Christ (Revelation 1:1). They are distinct persons. Since the New Testament is careful to draw a distinction between Jesus and the Father, so should we. On the other hand, it is also clear that the New Testament brings together Jesus Christ (the Son), the Father and Holy Spirit as they who act in eternal communion and oneness in everything, most notably in our salvation (Matthew 28:19; John 14:15-26).
When Christians confess Jesus Christ as true God of true God they also distinguish between the Father and Son and know them as distinct Persons. However, the Christian confession also recognizes that the Father, Jesus Christ the Son and the Holy Spirit are one divine union in that they are the three Persons of the one God, as he has revealed himself to be. So, we say there are three who are divine, yet only one God exists.
Christian theologians have agreed to apply the word “Persons” to each of the three, and the word “Being” to the One God. Hence, we confess that God is three Persons but One Being. The Father, the Son and Holy Spirit are the same in essence, thus they constitute the One God, but they are distinct in Person.
The Athanasian Creed, probably of the 5th century, describes the oneness and threeness of God in clear terms. It helps fix in our mind the difference between the oneness of essence and threeness of Person in the Godhead. Here is a portion of the Athanasian Creed:
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 Spirit. But the Godhead of the Father, of the Son, and of the Holy Spirit, is all one: the Glory equal, the Majesty coeternal. Such as the Father is, such is the Son, and such is the Holy Spirit. The Father uncreated, the Son uncreated, the Holy Spirit uncreated. The Father infinite, the Son infinite, and the Holy Spirit infinite. The Father eternal, the Son eternal, the Holy Spirit eternal. And yet they are not three eternals, but one eternal. As also there are not three uncreated, nor three infinites, but one uncreated, and one infinite. So likewise the Father is Almighty, the Son Almighty, and the Holy Spirit Almighty. And yet they are not three Almighties, but one Almighty. So the Father is God, the Son is God, and the Holy Spirit is God. And yet there are not three Gods, but one God.
The Trinity doctrine tells us that the Father, Son and Holy Spirit can be distinctly referred to, but they do not add up to three Gods. They exist together as the one true God. The Father, Son and Holy Spirit share one mutual existence through the one divine essence of which they are composed. Each of the Persons of the Trinity is identical as to essence, but the Persons can be distinguished, for God has revealed himself as three Persons.
We must remain humble and confess that neither biblical nor Trinitarian phrases explain how the three Persons can be one Being, only that it is so, according to what God has revealed of himself. Our confession of the Trinity is that of the testimony of Scripture, from which we understand that God is one divine Being who exists as or in three eternal, co-essential, yet distinct Persons – Father, Son and Holy Spirit.
This is the aspect of the Trinity that is a grand and divine mystery. It is a mystery because it is beyond our experience and vocabulary to try to image God as he is. In fact, Scripture cautions us not to attempt to image him by applying elements of our creaturely existence to God’s divine existence. All such images, whether in stone or in the imagination of the mind, are no more than idols.
Perhaps if we are careful in our usage, an analogy from our physical world can help us understand how God can be one and yet be three. Before we do, our caution bears repeating. Theologian Thomas Torrance explains that we must “reject any mythological projection by us into God of the creaturely relations and images latent in the natural and pre-theological significance of these concepts” (The Christian Doctrine of God: One Being, Three Persons, page 105). Having that caution squarely in mind, we can use the following image to understand something of how God can be both one Being and three Persons.
We learned in school that white light actually contains all the colors of the rainbow. There are three primary colors, which we name red, yellow and blue. Yet, these three primary colors are contained in the one light that is white light. The primaries do not exist apart from the white light, but co-inhere in it. At the same time, light as white light would not exist apart from the three primary colors. To speak of “light” is to speak of the three primaries, and yet each of the primaries is distinct from each other.
It’s the same with the one God who is called Father, Son, and Holy Spirit. Each Person of the Godhead is distinct but not separate. God exists only as the one God and can only be named as such because he is Triune in his One Being, existing eternally as Father, Son and Holy Spirit.
To God’s elect… who have been chosen according to the foreknowledge of God the Father, through the sanctifying work of the Spirit, for obedience to Jesus Christ and sprinkling by his blood” (1 Peter 1:1-2).