Albert Barnes Commentary Luke 24:19

"And he said unto them, What things? And they said unto him, The things concerning Jesus the Nazarene, who was a prophet mighty in deed and word before God and all the people:" — Luke 24:19 (ASV)

A prophet. A teacher sent from God. They did not then call him the Messiah, for his death had led them to doubt that, but they had no doubt that he was a distinguished prophet. The evidence of that was so clear that they could not question it.

Mighty in deed. Powerful in working miracles, in raising the dead, healing the sick, etc.

In word. In teaching.

Before God and all the people. Manifestly; publicly. So God acknowledged him, and the people regarded him as a distinguished teacher.

(Acts 7:22, regarding mighty.)