I note that he cannot tell where his "Christian" teaching came from concerning the "Trinity".
His belief does not agree with the Christians of old.
Maybe they weren't "Christians" either.
The first step is to establish the biblical doctrine that there is only one God. Then, you find that each of the persons is called God, each creates, each was involved in Jesus' resurrection, each indwells, etc. Therefore, God is one, but the one God is in three simultaneous persons. Please note that the idea of a composite unity is not a foreign concept to the Bible; after all, man and wife are said to be one flesh. The idea of a composite unity of persons is spoken of by God in Genesis (Gen. 2:24).
There is only one God
The first step is to establish how many Gods exist: one! Isaiah 43:10; 44:6,8; 45:5,14,18,21,22; 46:9; 47:8; John 17:3; 1 Cor. 8:5-6; Gal. 4:8-9
"I am the LORD, and there is no other; besides Me there is no God" (Isaiah 45:5).
“Thus says the Lord, the King of Israel And his Redeemer, the Lord of hosts: ‘I am the first and I am the last, And there is no God besides Me," (Isaiah 44:6).
"I am the Lord, and there is no other; besides Me there is no God, (Isaiah 55:5).
The Trinity
FATHER SON HOLY SPIRIT Called God: Phil. 1:2 John 1:1,14; Col. 2:9 Acts 5:3-4
Creator: Isaiah 64:8 John 1:3; Col. 1:15-17 Job 33:4, 26:13
Resurrects: 1 Thess. 1:10 John 2:19, 10:17 Rom. 8:11
Indwells: 2 Cor. 6:16 Col. 1:27 John 14:17
Everywhere: 1 Kings 8:27 Matt. 28:20 Psalm 139:7-10
All knowing: 1 John 3:20 John 16:30; 21:17 1 Cor. 2:10-11
Sanctifies: 1 Thess. 5:23 Heb. 2:11 1 Pet. 1:2
Life giver: Gen. 2:7: John 5:21 John 1:3; 5:21 2 Cor. 3:6,8
Fellowship: 1 John 1:3 1 Cor. 1:9 2 Cor. 13:14; Phil. 2:1
Eternal: Psalm 90:2 Micah 5:1-2 Rom. 8:11; Heb. 9:14
A Will: Luke 22:42 Luke 22:42 1 Cor. 12:11
Speaks: Matt. 3:17; Luke 9:25 Luke 5:20; 7:48 Acts 8:29; 11:12; 13:2
Love: John 3:16 Eph. 5:25 Rom. 15:30
Searches the heart: Jer. 17:10 Rev. 2:23 1 Cor. 2:10
We belong to: John 17:9 John 17:6 . . .
Savior: 1 Tim. 1:1; 2:3; 4:10 2 Tim. 1:10; Titus 1:4; 3:6 . . .
We serve: Matt. 4:10 Col. 3:24 . . .
Believe in: John 14:1 John 14:1 . . .
Gives joy: . . . John 15:11 John 14:7
Judges: John 8:50 John 5:21,30 . . .
Therefore, the doctrine of the Trinity is arrived at by looking at the whole of scripture, not in a single verse. It is the doctrine that there is only one God, not three, and that the one God exists in three persons: Father, the Son, and the Holy Spirit.