When the voice finished speaking, Jesus was there alone. They kept this to themselves, and didn't tell anyone at that time what they'd seen.
A time of tearing, and a time of mending. A time of keeping quiet, a time of speaking up.
As they descended the mountain Jesus gave them strict instructions. “Don't tell anybody what you saw until the Son of man has risen from the dead,” he told them.
(He really didn't know what to say because they were all so frightened!)