It was no small revolution that came in with Christ, and was preached by Paul; which was, indeed, entrusted and committed to him in a special way and made his "Stewardship". The implications are immensely and intensely challenging. Christendom has almost entirely failed to apprehend this change and its devastating implications. Hence, there is all the phraseology and terminology without the consistent nature and expression, and therefore without the impact and power or authority.
The "Mystery" - the eternal Divine secret - is still veiled in many hearts, even though they have the New Testament in their hands. It was because of this that the Apostle felt the need to pray for those who had received in word "the whole counsel of God" (Acts 20:27) that they might be given "a spirit of wisdom and revelation in the (full) knowledge of him, the eyes of (their) hearts being enlightened" (Eph. 1:17,18). If that were necessary then, is it less so now?