Ans: The Scriptures teach that there is one God who eternally exists in Three Persons.
Deut. 6:4. Hear, O Israel: The LORD our God is one LORD.
Matt. 28:19. Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.
See also: Gen. 1:1–3, 26–28; Isa. 44:6–8; 1 Cor. 8:4–6; Col. 2:9; 1 Tim. 3:16.
The term “Trinity” derives from the Latin trinitas, or “threeness,” from tres, three, and uno, one. The trinity or tri–unity of God is a great mystery. It is a Divinely–revealed truth because it is revealed only in the Scriptures and is received by faith. There is no analogy [corresponding truth or illustration] found in creation. Any attempt to illustrate the trinity or tri–unity of God from creation necessarily fails.
The truth of the Trinity can be seen as it is set forth from the Scriptures in four statements: God the Father is God (Matt. 11:25). God the Son [the Lord Jesus Christ] is God (Isa. 9:6; Jn. 1:1–3, 14, 18; Col. 2:9). God the Holy Spirit is God (Gen. 1:1–2; Acts 5:3–4; 2 Cor. 3:17). There is only One God (Deut. 6:4; Isa. 44:6–8; 1 Cor. 8:4–6).
There are two theological terms with which we ought to be familiar—the Ontological and Economic Trinity. These are two ways of viewing the one Trinity because of our finite comprehension. The word “ontological” means “being” [Gk. ontos, “being”], and refers to the Persons of the Godhead in their essence and relationship to one another. The word “economic” [Gk. oikonomia, “economy”] means “management” or “administration,” and refers to the Persons of the triune Godhead in their unified cooperation in the works of creation, redemption and providence. The terminology “Ontological Trinity” means that God has eternally existed in Three Persons. Some hold erroneously that God is only trinitarian in relation to the created universe. Such a view necessarily and inherently denies the Ontological Trinity and thus both the eternal Sonship of the Lord Jesus Christ and the personality of the Holy Spirit. See Questions 25 and 26.