One Three Person God
The Scriptures clearly indicate a belief in the worship of one true God alone. The belief in the existence of one God is called monotheism. Trinitarians insist they are monotheists and they do not believe in three Gods/gods but believe in one God consisting/subsisting of three persons.
The doctrine of the Trinity is most simply described as three persons in one God or one God in three persons, the belief in one distinct God subsisting as three distinct persons, namely, the Father, the Son, and the Holy Spirit. Trinitarians often express this belief in a variety of ways, "one God yet three persons," "three persons yet one God," "three persons one divine nature," "three persons yet one divine being," etc.
Trinitarian theologians often use the more technical Greek language terms hypostasis (pl. hypostases) and ousia. With respect to these terms, the doctrine of the Trinity is defined as "Three hypostases in one Ousia." In the fourth century, there was some confusion concerning these particular terms. The Trinitarian definition of these terms was established in terms of the doctrine of the Trinity itself during this time period. The word hypostasis refers to each of these three distinct persons. This particular word is used in reference to the "threeness" of God since there are three hypostases. The word ousia is used in reference to the "oneness" of God. Each hypostastis has the "same being" or "same substance" which is knownn by the technical term homoousia. The Triune God is three hypostases where each hypostasis has an identical ousia (being/substance). The equivalent Latin based term is "consubstantial."
There is no real need to employ these technical terms since the doctrine of the Trinity is most commonly described as three persons in one divine nature by Trinitarians themselves. Trinitarians believe that each of these three hypostases are a person and the terms "person" and "hypostasis" are used synonymously. This is evidenced by their argument that the Holy Spirit is indeed a distinct third person in addition to the Father and the Son. It is also evidenced when Trinitarians insist the Father and the Son are indeed distinct and separate persons in reaction to Modalism.
Another description they like to use is the term "Triune God" from "Tri" and "Unity." The word "Trinity" is actually derived from the word "tri" and "unity" and so Trinitarians use this word meaning "tri-unity" or "tri-oneness." The intent of this term is to denote the unity, or oneness, of divinity or substance of being between the three persons, Father, Son, and Holy Spirit. The Father is not the Son and the Father is not the Holy Spirit and the Son is not the Father and is not the Holy Spirit and the Holy Spirit is not the Father and not the Son. Yet, all are God and all are coeternal, co-equal, co-powerful.
Trinitarians insist they are monotheistic and not henotheistic or polytheistic. They do not claim the Father, Son, and Holy Spirit are three Gods/gods, but one God, nor do they say they believe in three Gods/gods in one God but simply one God. These three persons constitute the one God. Trinitarians will [usually] insist God is not simply one person because, to the contrary, God is not one person but three persons and then they would be bound to say God is three persons in one person which they do not wish to do. So they also sometimes like to say that God is indeed "one being" althought God is three "persons." A term they sometimes use is "tripersonal God" where God is one tripersonal being. As such, Trinitarians do not see themselves as polytheists, or more specifically, tritheists. Rather they see themselves as monotheists who believe in a multi-personal one being God.
The doctrine of the Trinity is not explicitly taught in the Scriptures or the writings of the ante-Nicene church Fathers. Trinitarians believe their doctrine is inferred in the Scriptures and known through their process of reason from analyzing certain statements found in the Scriptures. The following illustrates the basic structure of their reasoning.
Premise 1: The Bible teaches that there is only one God.
Premise 2: The Bible teaches that there are three distinct persons called God, known as the Father, Son, and Holy Spirit.
Conclusion: The three persons, Father, Son, and Holy Spirit are the one God.
It is the second premise which non-trinitarians contest. Non-trinitarians do not agree that the Bible identifies the Son as the one "God." Non-trinitarians do agree that the Holy Spirit is God because the Holy Spirit is the spirit of the one Holy God. In other words, non-Trinitarians do not agree that the Holy Spirit is a separate person distinct from God the Father. Non-trinitarians insist that God is one person, the Father, and Jesus is the son of that one God, the Father, and the Holy Spirit is the spirit of the one Holy God, the Father.
Trinitarianism and Modalism
The doctrine of the Trinity is often confused with a view of God known as Modalism and even the most astute Trinitarians can be found inadvertently promoting Modalist beliefs. To many people, Modalism can appear very similar to Trinitarianism. Modalism is also known as Sabellianism and colloquially known as "Oneness Theology" and sometimes "Jesus only." In Trinitarianism, the Father is not the Son and the Son is not the Father. However, in Modalism, the Father is the Son and the Son is the Father. In Trinitarianism, God is not one person but three persons. However,in Modalism God is one person and not three persons. God is one person and that one person is Jesus and Jesus is the Father and Jesus is the Son and as such is God who manifests himself differently in these ways. In this belief system, the three distinctions of God are not personal distinctions of one being but functional distinctions one person. Hence, the distinctions of "Father," and "Son" are different functional modes of being of the same person.
I ran across a website the other day where a lady wished to defend the Trinity. She used an analogy to describe her belief and explained that although she is one person, she is a wife and a mother and a daughter. She was completely unaware that she was promoting simultaneous Modalism which is considered heresy among Trinitarians. I ran across another Eastern Orthdox website which indicated that God had manifested himself in three different ways throughout history, first as Father, then as Son, and now as Holy Spirit. This is not Trinitarianism but successive Modalism, another concept considered to be heretical by Trinitarians. In Modalism, God is one person who is manifested in different modes or functional offices such as Father and Son. This confusion is common even within Trinitarianism. It is actually quite common to find trained Trinitarian theologians waist deep in Modalist waters in efforts to explain their own Trinitarian doctrine. The reason this confusion exists is that both Trinitarians and Modalists can, and do, say the one God is manifested, or expressed, in three different ways, three different distinctions. The Trinitarian modes are the modes of three distinct persons of the one God, while the Modalist mode are the modes of three distinct "functions" or modes of being of the one God. When examined closely, Modalism and Trinitarianism essentially differ in one simple aspect. The Modalist believes in one person manifesting as three distinct beings. The Trinitarian believes in one being manifesting as three distinct persons. If a person was to equate the concept of "being" and "person" there is then no real difference between the two. However, this is where the hair-splitting begins. Modalism was actually the first concerted philosphical attempt in church history to try and explain the relationship between Father, Son and Holy Spirit and the breeding ground for what later became Trinitarian theology as a reaction to Modalism (Arianism was also a reaction to perceived Modalism). The Modalist Supreme identity is one person. The Trinitarian Supreme identity is one being. The Modalist Supreme identity is manfested in three functional offices, Father, Son, Holy Spirit. The Trinitarian Supreme identity also functions as three distinctions, Father, Son, Holy Spirit. It is very interesting to compare Modalist and Trinitarian statements and one finds each of them often dipping into each other's theological candy jar when it becomes necessary for them to do so. The doctrine of the Trinity does not, on one hand, assert that three persons are united as one person, or three beings in one being. The doctrine of the Trinity does, on the other hand, assert that three persons are united as one being, or one being as three persons. In each case, Modalists and Trinitarians are trying to preserve the idea that God is one identity or one individual without getting caught in a false teaching.
The important thing to remember here is that Trinitarians vehmently reject Modalism as heresy. When Trinitarianism is challenged one must be sure that one is not really objecting to Modalism and this is a very common mistake. However, one must also be reminded that Trinitarians very often misrepresent Modalists due to either ignorance or simply an overzealousness to assault their belief system. And very often Modalists do the very same thing to Trinitarians. Modalism does not have a very wide following and is mostly confined to distinct groups within pentecostalism such as the United Pentecostals (the majority of other Pentecostals, such as Assemblies of God, are Trinitarians).
Economic Unity: Your Trinity and Mine
The early church understood an "economic unity" existed between God, the Son, and the Holy Spirit. This is simply a way of saying the three had a unity of function between them which we must understand should not be confused with a unity of substance / being. Economic unity is about doing not being. Trinitarian historians sometimes conveniently refer to this concept as "Economic Trinitarianism," a term which is somewhat misleading to the unwary reader. In the Trinitarian psyche, this "economic trinitarianism" is a primitive form of his own more highly developed dogma. However, this economic unity is recognized by Trinitarians and non-Trinitarians alike. An Arian, or Jehovah's Witness, or most other non-trinitarians do not have any problem recognizing there are three defined entities and a unified functional relationship exists between those three. In this sense of the word, everyone agrees there is a "trinity" of three. And the non-trinitarian realizes this does not amount to Trinitarian dogma. For some reason, many Trinitarians do not quite comprehend this fact. Economic unity, or economic trintarianism, is about "function" and not "substance/being." It is a concept which does not emphasize "being" but "doing." It is a verb thing and not a noun thing. The issue with Trinitarianism is whether or not the three constitute one being known as "God." For the Trinitarian, it is a matter of "being" God inherently (ontologically), not simply doing "God" functionally (economically). It is a question of identity and nature. For the non-Trinitarian, the three have a unified purpose and function and there is no reason seen to conclude the three should be understood as a three in one being called "God." The non-Trinitarian recognizes the early Fathers saw a relationship between the three and just one of those three was actually God, and God being already identified, he sees no reason whatsoever to label all three together as "God."
Jesus functioned according to God the Father in the Spirit. We, the church, the body of Christ, are now to do the very same thing. Jesus prayed for this functional, that is, economic unity between God, the church, and himself. This unity of purpose is an economic unity. Jesus taught that he and his father were one and then later prayed that the church would be one with him and the Father, "just as we are one." He was referring to functional unity in both instances. It is the Spirit which unified him with his Father in what he did and it is the Spirit which unifies us with God and Jesus in what we do. "Those who are being led by the Spirit of God, these are sons of God" (Rom 8:14). After he rose from the dead, Jesus called his disciples and said, "As the Father sent me, now I also send you.... Receive the Holy Spirit." That economic unity exists between the Father, Son, and Holy Spirit. Jesus prayed for a unity between the Father, the Church in which the Spirit dwells, and himself in this sense. In this same sense, God the Father, the Son, and the church, are a "trinity" because there are three and they have an economic unity in function. However, to define all three as the one God is quite another matter. And this is the distinction we must see here. Trinitarians often disingenuously make huge unwarranted leaps by trying to persuade others that the early Christians were "Trinitarians" simply because they believed in an economic unity which is simply a unity of function.
We must understand that an economic unity between God, Jesus, and the Holy Spirit, does not amount to Trinitarian dogma. It is very common for Trinitarians to read passages like Matthew 28:19, 2 Corinthians 13:14, and 2 Peter 1:2 and suppose the writers are here referring to their "three in one God." However, all all we have is God mentioned with two other entities, Jesus, and the Holy Spirit. The non-Trinitarian has no problems with these passages. In fact, he has less problems. All they need to do is recognize that God is mentioned along with two other entities. In the end, only one of them is "God," not all three together. The Trinitarian needs to first define the word "God" in his mind as "the Father, the first person of the Trinity," and then extraneously decide for himself to label the one already called "God" as "the Father, the first person of the Trinity," and then think of the other two as "second and third persons of the Trinity" and then label all three together as "God" by an act of His own will. These mental gymnastics are standard fare for Trinitarians and it is something the non-Trinitarian does not need to do and the Bible never does either. The non-trinitarian simply accepts what it says and sees that the one God of creation is mentioned along with two other entities. The early fathers viewed God in a similar manner and perceived of an economic unity, or an "economic trinity," between God, His Son, and His Holy Spirit, just as there is an economic unity between God, Jesus and the church where the Holy Spirit lives. However, this does not amount to Trinitarian dogma which insists God is a ontological unity of substance, that is, God is three persons but one being.