After six days Jesus took Peter, James, and John and led them up a high mountain apart by themselves. And he was transfigured before them, and his clothes became dazzling white, such as no fuller on earth could bleach them. Then Elijah appeared to them along with Moses, and they were conversing with Jesus. Then Peter said to Jesus in reply, “Rabbi, it is good that we are here! Let us make three tents: one for you, one for Moses, and one for Elijah.” He hardly knew what to say, they were so terrified. Then a cloud came, casting a shadow over them; then from the cloud came a voice, “This is my beloved Son. Listen to him.” Suddenly, looking around, they no longer saw anyone but Jesus alone with them.
As they were coming down from the mountain, he charged them not to relate what they had seen to anyone, except when the Son of Man had risen from the dead. So they kept the matter to themselves, questioning what rising from the dead meant. Then they asked him, “Why do the scribes say that Elijah must come first?” He told them, “Elijah will indeed come first and restore all things, yet how is it written regarding the Son of Man that he must suffer greatly and be treated with contempt? But I tell you that Elijah has come and they did to him whatever they pleased, as it is written of him.”Mark 9:2-13
Preaching the transfiguration of a dead man is a dead end.
Divine wisdom forbade Peter, James and John from proclaiming to the world their vision of Christ’s transfiguration until after the resurrection when his glory was sealed.
The spectacle of the Father’s “beloved Son” hanging on the cross frightened all the disciples away except John. Any testimony of the transfiguration prior to the crucifixion would have been discredited and mocked.