Summary: Trinitarian doctrine
What is the doctrine of the Trinity? It should be noted that the word Trinity is never given in the Bible; it was originally used by the church father Tertullian (AD 155–220).” “The word trinity means ‘tri-unity’ or ‘three-in-oneness.’ It is used to summarize the teaching of Scripture that God is three persons yet one God.” Essentially, the doctrine of the Trinity teaches these three things:
1. There is one God
2. God is three individual persons and each is fully God.
3. God is a unity (three-in-oneness)
The Westminster Confession of Faith (1647) summarizes these statements this way: “In the unity of the God-head there be three persons, of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost.”
These truths seem to contradict one another. How can there be one God and, yet, three individual persons that are also fully God? It is not something that we necessarily fully understand, but it is something the Bible teaches. J. I. Packer said this:
The historic formulation of the Trinity...seeks to circumscribe and safeguard this mystery (not explain it; that is beyond us), and it confronts us with perhaps the most difficult thought that the human mind has ever been asked to handle. It is not easy; but it is true.
Let’s investigate each of these statements regarding the doctrine of the Trinity.
Where do we see the teaching that we have one God? We see it throughout the Old Testament. In fact, this was the teaching that at that time separated Judaism from other religions. Monotheism during ancient times was unique, as most nations accepted many gods.
We see this in Deuteronomy 6:4–5: “Hear, O Israel: The LORD our God is one LORD: And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might” (emphasis mine).
The great declaration of the Jewish religion was that God was one Lord, and on that basis, he should be loved with all one’s heart, soul, and might. He was the only one worthy of worship because he was the only God. In fact, we see this reiterated by implication in the Ten Commandments through the prohibition against idols.
I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage. Thou shalt have no other gods before me. Thou shalt not make unto thee any graven image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me. (emphasis mine)
The implication is that God is the only God, and therefore, the Israelites should not worship other gods or make any idols before him. God is one.
We also see this teaching throughout the New Testament. James declares this in James 2:19: “You believe that there is one God. Good! Even the demons believe that—and shudder” (emphasis mine).