Jesus said to his disciples: If any man will come after me, let him deny himself, and take up his cross, and follow me. For he that will save his life, shall lose it: and he that shall lose his life for my sake, shall find it (Matthew 16:24-25).
Jesus sets before Peter, James and John…these persons – Moses and Elijah.
Each of these, having lost his life, found it. For each of them both spake boldly unto tyrants, Moses to the Egyptian, Elijah to Ahab; and in behalf of heartless and disobedient men; and by the very persons who were saved by them, they were brought into extreme danger; and each of them wishing to withdraw men from idolatry.
[...] What if Moses clave a sea? Peter walked on the water, and was able to remove mountains, and used to work cures of all manner of bodily diseases, and to drive away savage demons, and by the shadow of his body to work those wonderful and great prodigies; and changed the whole world. And if Elijah too raised a dead man, yet these apostles raised ten thousand….
He brings them forward accordingly for this cause also. For He would have them emulate their winning ways toward the people, and their presence of mind and inflexibility; and that they should be meek like Moses, and jealous for God like Elijah, and full of tender care, as they were. For Elijah endured a famine of three years for the Jewish people; and Moses said, “If thou wilt forgive them their sin, forgive; else blot me too out of the book, which thou hast written.”
Now of all this He was reminding Peter, James and John by the vision. For He brought those in glory too, not that these should stay where they were, but that they might even surpass their limitary lines. [...] For “except your righteousness shall exceed the righteousness of the Scribes and Pharisees, ye shall in no case enter into the kingdom of Heaven.”
For not into Egypt did they enter, but into the whole world, worse disposed than the Egyptians; neither were they to speak with Pharaoh, but to fight hand to hand with the devil, the very prince of wickedness. Yea, and their appointed struggle was, both to bind him, and to spoil all his goods; and this they did cleaving not the sea, but an abyss of ungodliness, through the rod of Jesse,—an abyss having waves far more grievous.
See at any rate how many things there were to put the men in fear; death, poverty, dishonor, their innumerable sufferings…. But nevertheless against all these things He persuaded them boldly to venture, and to pass as along dry ground with all security. To train them therefore for all this, He brought forward those who shone forth under the old law.