As
a matter of fact the Old Testament contains not only mere “indications” of the
Holy Trinity, but clear passages in which the doctrine is unmistakably set
forth. Such passages are those: a) in which God speaks of Himself in the plural
number, Gen. 1, 26; b) in which the Lord speaks of the Lord, Gen. 19, 24; c) in
which the Son of God is expressly named, Ps. 2, 7; d) in which three Persons of
the Godhead are distinctly enumerated, Gen. 1, 1. 2; 2 Sam. 23, 2; Ps. 35, 6;
Is. 42, 1; 48, 16. 17; 61, 1; e) in which the name Jehovah or God is thrice repeated
in the same relation, Num. 6, 24-26; Ps. 42, 1, 2; Is. 33, 22; Jer. 33, 2; Dan.
9, 19; f) from the trisagion of the angels, Is. 6, 3; g) from the passages in
which the Angel of the Lord (מַלְאַךְ יְהוָה) is identified with God, Gen. 48,
15. 16; Ex. 3, 1-7; h) from the reference of Christ to the Old Testament when
HE proved the true deity and divine personality of the Son of God, Matt. 22,
41-46 compared with Ps. 110, 1. Certainly no one has ever been saved who did
not believe in the true God (The Triune God) and the true Savior of the world
(the Second Person of the Godhead), since this truth is stated so clearly in
Scripture, Acts 4, 12; John 5, 23; 1 John 2, 23. Nor is the plan of salvation
which is taught in the New Testament different from that which was taught in
the Old Testament, Rom. 3, 21-34; 4, 1-3. We rightly hold therefore that the
doctrine of the Holy Trinity is so clearly set forth in the Old Testament that
the believers in the Old Testament most assuredly had a true knowledge of God and
of the promised Savior, His beloved Son. (John Theodore Mueller, Christian
Dogmatics: A Handbook of Doctrinal Theology for Pastors, Teachers, and Laymen
[St. Louis: Concordia Publishing House, 1934], 159-60)