The doctrine of the Trinity is, in its last analysis, a deep mystery
that cannot be fathomed by the finite mind. That it is taught
in the Scripture, however, there can be no reasonable doubt. It
is a doctrine to be believed even though it cannot be thoroughly
understood.
a) The Doctrine of the Trinity in the Old Testament.
This doctrine is not so much declared as intimated in the Old
Testament. The burden of the Old Testament message seems to be the
unity of God. Yet the doctrine of the Trinity is clearly intimated
in a four-fold way:
First: In the plural names of the Deity; e. g., Elohim.
Second: Personal pronouns used of the Deity. Gen. 1:26; 11:7;
Isa.6:8.
Third: The Theophanies, especially the "Angel of the Lord." Gen.16
and 18.
Fourth: The work of the Holy Spirit. Gen. 1:2; Judges 6:34.
b) The Doctrine of the Trinity in the New Testament.
The doctrine of the Trinity is clearly taught in the New Testament;
it is not merely intimated, as in the Old Testament, but explicitly
declared. This is evident from the following:
First: The baptism of Christ: Matt 3:16, 17. Here the Father speaks
from heaven; the Son is being baptized in the Jordan; and the Spirit
descends in the form of a dove.
Second: In the Baptismal Formula: Matt. 28:19--"Baptizing them in
the name (sing.) of the Father, and of the Son, and of the Holy
Ghost." Third: The Apostolic Benediction: 2 Cor. 13:14--"The grace
of our Lord Jesus Christ....love of God.....communion of the Holy
Ghost."
Fourth: Christ Himself teaches it in John 14:16--"_I_ will
pray the _Father_... He will give you another _Comforter_."
Fifth: The New Testaffignt sets forth:
A Father who is God, Rom. 1:7.
A son who is God, Heb. 1:8.
A Holy Spirit who is God, Acts 5:3, 4.
The whole is summed up in the words of Boardman: The Father is all
the fulness of the Godhead invisible, John 1:18; the Son is all
the fulness of Godhead manifested, John 1:4-18; the Spirit is all
the fulness of the Godhead acting immediately upon the creature,
1 Cor. 2:9, 10.