The multitude were favourably towards Jesus, and were glad that returned at an opportune moment to defend his disciples against the scribes. But why were they greatly amazed? The word in the Greek is ἐξεθαμβήθη.
It seems most probable that they saw in his countenance, always heavenly and majestic, something even yet more Divine, retaining some traces of the glory of his transfiguration, even as the face of Moses shone when he came down from the mount (Exodus 34:29).
It hardly seems likely that the amazement of the people was simply caused by our Lord having arrived at an opportune time to relieve his disciples of their difficulty. The Greek word expresses something more than would be satisfied by the fact of our Lord having come upon the scene just when he was wanted.
Even if there were no remains of the transfiguration glory upon his countenance, the vivid recollection of the scene, of the conversation with Moses and Elijah, and the subject of it, and the voice of the Father, must have invested his countenance with a peculiar majesty and dignity.
The same word, though without its compound ( ἐθαμβοῦντο), is used further on in Mark 10:32 to express the amazement of the disciples, as he pressed eagerly onwards before them on his way to Jerusalem and to his cross.
There was no doubt something then in his countenance which astonished them. The multitude running to him, saluted him. The scribes had not been able to shake their faith. In their view he was still "that Prophet that should come into the world."