Now, I love this priest so I'm not being critical, but my immediate reaction was, "Oh, come on, Father. Even I know that one. No way!"
Think about the scene. Jesus knows what is coming; He's going to undergo horrific suffering which, in His humanity, had to strike hard at His heart. He also knows that even His closest disciples were almost totally clueless. But the Father had a plan. Like so many things God does, it wasn't going to make much sense at all to those disciples at the time. God seems to like to plant things in our lives that only make sense after all the pieces of His plan come together. He does this so that eventually we learn to have faith when we can only see part of something.
Jesus is on the mountain, Moses and Elijah appear, and suddenly He is revealed in His heavenly glory. And Peter, James and John witness it.
Mark's gospel has it that they were "exceedingly afraid." Matthew says they fell face down because they were overwhelmed by awe.
The glory of God appears, and the response is fear. It happens over and over again in the Bible. This is why the angels are always saying, when they appear to folks, "Fear not!"
Now, these days God's normal plan is not to send angels to manifest themselves visibly to people so that His glory can be known. No, His plan is even weirder than that. "All of us, gazing with unveiled face on the glory of the Lord, are being transformed into the same image from glory to glory, as from the Lord who is the Spirit" (2 Cor. 3:18).
You see, Christ has died, Christ is risen, Christ will come again. And we are baptized into Him, and we receive and behold His glory, not as the Israelites did (and that was glorious enough, St. Paul tells us), but like that Mount of Transfiguration. We see with eyes of faith. Faith is not mere intellectual assent to what the Bible says or what the Catechism teaches. Faith is the head and heart in a union that says "Yes, it is true" and "Here I come!" as I fling my whole life into God's hand at His bidding.
Flinging ourselves, that is, real faith, is scary. The glory of God is scary. Seeing God revealed is scary. Hearing His call is scary. Witnessing Truth, Beauty, and Goodness alive and at work in our midst is scary.
I love Peter's reaction to this scary situation. He starts blurting stuff out. He must have been an extrovert. It is almost as if the words out of his mouth about building these booths were like a buffer he tried to throw up in order to protect his soul from the scariness, to keep it at a manageable distance from himself.
But he need not have worried, because the scary thing passed, and the disciples were left seeing Jesus only. And they were charged not to mention it until after Jesus rose from the dead. Talk about adding mystery on to scariness. I love that line in Mark's gospel after Jesus said this, "They discussed among themselves what 'rising from the dead' meant." They couldn't even get that, let alone why they weren't supposed to say anything about this bizarre experience that they couldn't begin to take in.
There was a work this experience had to do inside these men. They had to figure out how to respond to it. It had to eat away at them like some kind of a purification. Eventually, they needed to respond in faith. I wonder if Peter and John thought of this, or mentioned it to each other, as they were running to the tomb on Easter morning, or on the way back. "Hey, remember that day on Mt. Tabor? Remember how Jesus said we shouldn't tell anyone until He rose from the dead?" I wonder if perhaps John's response to Tabor was what helped him show up at the crucifixion. Eventually, though, all the pieces fit together, faith blossomed, the Holy Spirit empowered their understanding, and Peter, James and John each in their own way embraced their own share of the Lord's passion, and taught other believers to do the same.
Talk about needing to completely recalibrate one's life. The glory of God appearing has a way of making huge demands on us, because suddenly we have light and can see reality. We need to choose whether to stay with the gloriously terrifying light or to revert to the now-dissatisfying dismal murk of life in the world and the flesh. It is good for us that the glory of God is even more attractive than it is terrifying.
P.S. One of my all-time favorite songs for good measure.