The doctrine of the Trinity is very decidedly a doctrine of revelation. It is true that human reason may suggest some thoughts to substantiate the doctrine, and that men have sometimes on purely philosophical grounds abandoned the idea of a bare unity in God, and introduced the idea of living movement and self-distinction. And it is also true that Christian experience would seem to demand some such construction of the doctrine of God. At the same time it is a doctrine which we would not have known, nor have been able to maintain with any degree of confidence, on the basis of experience alone, and which is brought to our knowledge only by God’s special self-revelation. Therefore it is of the utmost importance that we gather the Scriptural proofs for it.
a. Old Testament proofs. Some of the early Church Fathers and even some later theologians, disregarding the progressive character of God’s revelation, gave the impression that the doctrine of the Trinity was completely revealed in the Old Testament. On the other hand Socinians and Arminians were of the opinion that it was not found there at all. Both were mistaken. The Old Testament does not contain a full revelation of the trinitarian existence of God, but does contain several indications of it. And this is exactly what might be expected. The Bible never deals with the doctrine of the Trinity as an abstract truth, but reveals the trinitarian life in its various relations as a living reality, to a certain extent in connection with the works of creation and providence, but particularly in relation to the work of redemption. Its most fundamental revelation is a revelation given in facts rather than in words. And this revelation increases in clarity in the measure in which the redemptive work of God is more clearly revealed, as in the incarnation of the Son and the outpouring of the Holy Spirit. And the more the glorious reality of the Trinity stands out in the facts of history, the clearer the statements of the doctrine become. The fuller revelation of the Trinity in the New Testament is due to the fact that the Word became flesh, and that the Holy Spirit took up His abode in the Church.
Proof for the Trinity has sometimes been found in the distinction of Jehovah and Elohim, and also in the plural Elohim, but the former is entirely unwarranted, and the latter is, to say the least, very dubious, though Rottenberg still maintains it in his work on De Triniteit in Israels Godsbegrip.[pp. 19ff.] It is far more plausible that the passages in which God speaks of Himself in the plural, Gen. 1:26; 11:7, contain an indication of personal distinctions in God, though even these do not point to a trinity but only to a plurality of persons. Still clearer indications of such personal distinctions are found in those passages which refer to the Angel of Jehovah, who is on the one hand identified with Jehovah, and on the other hand distinguished from Him, Gen. 16:7-13; 18:1-21; 19:1-28; Mal. 3:1; and also in passages in which the Word or Wisdom of God is personified, Ps. 33:4, 6; Prov. 8:12-31. In some cases more than one person is mentioned, Ps. 33:6; 45:6, 7 (comp. Heb. 1:8, 9), and in others God is the speaker, and mentions both the Messiah and the Spirit, or the Messiah is the speaker who mentions both God and the Spirit, Isa. 48:16; 61:1; 63:9, 10. Thus the Old Testament contains a clear anticipation of the fuller revelation of the Trinity in the New Testament.
b. New Testament proofs. The New Testament carries with it a clearer revelation of the distinctions in the Godhead. If in the Old Testament Jehovah is represented as the Redeemer and Saviour of His people, Job. 19:25; Ps. 19:14; 78:35; 106:21; Isa. 41:14; 43:3,11,14; 47:4; 49:7,26; 60:16; Jer. 14:3; 50:14; Hos. 13:3, in the New Testament the Son of God clearly stands out in that capacity, Matt. 1:21; Luke 1:76-79; 2:17; John 4:42; Acts 5:3; Gal. 3:13; 4:5; Phil. 3:30; Tit. 2:13,14. And if in the Old Testament it is Jehovah that dwells among Israel and in the hearts of those that fear Him, Ps. 74:2; 135:21; Isa. 8:18; 57:15; Ezek. 43:7-9; Joel 3:17,21; Zech. 2:10, 11, in the New Testament it is the Holy Spirit that dwells in the Church, Acts 2:4, Rom. 8:9,11; I Cor. 3:16; Gal. 4:6; Eph. 2:22; Jas. 4:5. The New Testament offers the clear revelation of God sending His Son into the world, John 3:16; Gal. 4:4; Heb. 1:6; I John 4:9; and of both the Father and the Son, sending the Spirit, John 14:26; 15:26; 16:7; Gal. 4:6. We find the Father addressing the Son, Mark 1:11; Luke 3:22, the Son communing with the Father, Matt. 11:25,26; 26:39; John 11:41; 12:27,28, and the Holy Spirit praying to God in the hearts of believers, Rom. 8:26. Thus the separate persons of the Trinity are made to stand out clearly before our minds. At the baptism of the Son the Father speaks from heaven, and the Holy Spirit descends in the form of a dove, Matt. 3:16,17. In the great commission Jesus mentions the three persons: “. . . baptizing them into the name of the Father and of the Son and of the Holy Spirit,” Matt. 28:19. They are also named alongside of each other in I Cor. 12:4-6; II Cor. 13:14; and I Peter 1:2. The only passage speaking of tri-unity is I John 5:7 (Auth. Ver.), but this is of doubtful genuineness, and is therefore eliminated from the latest critical editions of the New Testament.