Christ said "Likewise shall also the Son of man suffer of them" but they did not understand

Matthew 17:9- 13 Jesus charged them, saying tell no man the vision (Christ was transfigured before, Peter, James and John on the mount) And his disciples asked him, saying, Why then say the scribes that Elias must first come?

And Jesus answered and said unto them, Elias truly shall first come, and restore all things, but I say unto you that Elias has come already, and they knew him not, but have done unto him whatsoever they listed. Likewise shall also the Son of man suffer of them.

Then the disciples understood that he spake unto them of John the Baptist.

We are told that the word elias means forerunner. Elias the prophet (and many others) had prophesized of Christ’s birth. You may remember that when the angle Gabriel came to Mary with the news that she would bear the Son of God he also told her that her cousin Elisabeth was in the sixth month with a son. Remember how Mary went to visit her cousin and when Elizabeth heard Mary’s salutation, the babe, who was to be named John, leap for joy in her womb.  So John was on the earth at the same time period as Christ and was the forerunner or, prepared the way for Christ ministry.

Christ is trying in the experience on the mount to prepare Peter, James and John for his pending atonement, death and resurrection. To prepare these three for their role in continuing His church, but they do not understand the time frame here. They did not understand that the restoration would not happen in their dispensation – that there would be an apostasy – a falling away first. Do we? Do we understand that before Christ comes the second time there must be a restoration and an elias? Do we understand that that gathering has already begun? That Christ lives? That his church is now upon the earth?