Divine truth is the declaration of the councils of God (Acts 20:27) and all of that truth is in the Person of Christ as the sacred Repository and Treasure, and in Him they are to be learned.
So He testifies of himself, " I am the Truth. "John 14:6 He is the Truth Essentially, as he is One with the Father, the God of Truth. Deuteronomy 32:4. (Not just “about” the Father)
He is the Truth Efficiently, as by Him alone the Truth is fully and effectually declared. For no man has seen God at any time, the only begotten Son Who is in the Bosom of the Father has declared Him. John 1:18
He is the Truth Substantially, as opposed to the mere types and shadows of the Old testament for in Him dwells all the fullness of the Godhead bodily. Colossians 2:9.
He is Truth Subjectively, for all Divine truth relating to the saving knowledge of God is treasured up in Him. In Him are hid all the treasures of wisdom and knowledge, that is the wisdom and knowledge of God in His counsel's concerning the duty, the sanctification, and the salvation of the church. Colossians 2:3
Ephesians 3:8 speaks of this Truth as the unsearchable riches of God. These precious unsearchable treasures of the wisdom and knowledge of God, that is all Divine supernatural truths, are HID and safely deposited in Christ in and from whom ALONE they are to be learned and received.
So we are said to learn the Truth as it is in Jesus, Ephesians 4:21. Whatever notional knowledge men may have of Divine Truth, as they are doctrinally proposed in the scriptures yet, if they know them not in their respect unto the Person of Christ as the Foundation of the council of God, if they discern not how they proceed from Him and center in Him, these truths will bring no spiritual saving light unto their understanding for all spiritual life and light is in Him and from Him alone.
(Edited for modern comprehension, capital letters added for emphasis.)