Of course His sacrifice was "retroactive." Remember St. John Chrysostom's Paschal (Easter) homily Kolo posted so many times? Remember the icon of Christ breaking down the gates of hell and pulling out of the hands of death the OT righteous? (that's not biblical though!).
My point was that until His sacrifice on the cross, no one was saved. But He made it possible for the whole world to be saved, past, present and future.
My only problem is with the appearance of Moses at Mt. Tabor.
So, are you saying that Jesus did not sacrifice for Abraham, Isaac, Jacob, and all the prophets? Is there really more than one way to get to Heaven?
No & no. :)
Your first sentence is within time, but your second is not. If, to borrow a phrase :), "all time for God is NOW", which I have never disputed, then Jesus on the cross "happened" across all time. Therefore, why can't His sacrifice be in effect within time for all the OT righteous at the time they were alive?
My only problem is with the appearance of Moses at Mt. Tabor.
There it is. You raise an excellent point. If the sacrifice applied to Moses when he lived, then he would have been eligible to make that appearance.