Douglas Wilson is not afraid of big statements:
In short — and I speak reverently — Christ is the door to all of life, which means that He is the door to the Old Testament. And those who don’t want to enter by that door are thieves and robbers. But take it a step further. If Christ is the door to the Old Testament, Paul is the key.
Read how Wilson arrives at this statement here: Paul is the Key.
This statement is not problematic for anyone who knows that the Spirit of Christ moved Paul to write that which we read in the Scriptures.