It is an old saying that what becomes patent in the New Testament was latent in the Old Testament. And it is important that the continuity of the revelation of God contained in the two Testaments should not be overlooked or obscured. If we find some difficulty in perceiving for ourselves, in the Old Testament, definite points of attachment for the revelation of the Trinity, we cannot help perceiving with great clearness in the New Testament abundant evidence that its writers felt no incongruity whatever between their doctrine of the Trinity and the Old Testament conception of God. The New Testament writers certainly were not conscious of being “setters forth of strange gods.” To their own apprehension they worshipped and proclaimed just the God of Israel; and they laid no less stress than the Old Testament itself upon His unity (Jn. 17:3; 1 Cor. 8: 4; 1 Tim. 2:5). They do not, then, place two new gods by the side of Jehovah as alike with Him to be served and worshipped; they conceive Jehovah as Himself at once Father, Son and Spirit.
In presenting this one Jehovah as Father, Son and Spirit, they do not even betray any lurking feeling that they are making innovations. Without apparent misgiving they take over Old Testament passages and apply them to Father, Son and Spirit indifferently. Obviously they understand themselves, and wish to be understood, as setting forth in the Father, Son and Spirit just the one God that the God of the Old Testament revelation is; and they are as far as possible from recognizing any breach between themselves and the Fathers in presenting their enlarged conception of the Divine Being. This may not amount to saying that they saw the doctrine of the Trinity everywhere taught in the Old Testament. It certainly amounts to saying that they saw the Triune God whom they worshipped in the God of the Old Testament revelation, and felt no incongruity in speaking of their Triune God in the terms of the Old Testament revelation. The God of the Old Testament was their God, and their God was a Trinity, and their sense of the identity of the two was so complete that no question as to it was raised in their minds.