Seriously, I'm not sure why the almighty choose to reveal some of the mystery, but not all of it at once. Much still remains a mystery. We have to go by what we've been given. We are promised more will be revealed in the end. Maybe our puny brains just can't handle it all, or maybe it has to be kept a secret from the evil which now rules this world?
I think He HAS already revealed the Mystery to us. It was given as a series of revelations from the risen Christ to Paul, the person chosen by Christ to reveal the Church the BOdy of Christ and this dispensation of Grace that we now live in. Remember, Paul said he was given revelations (plural) and that we were to follow him as he followed Christ. All that we need to know about this age of the grace of God and reconciliation to Him have been divulged. IMHO. We’re just awaiting the final member of the Body to be saved and brought into the Body. Then we’re gone. And it’s off to the tribulation for the unbelievers. That’s what Romans through Philemon teaches us. BTW: nowhere else in the Bible talks about this time of the grace of God. Why? Because it was a mystery, a secret, hid in God since the foundation of the world, until revealed to Paul. See how succinctly and perfectly His Word fits?!