A prophet - A teacher sent from God. They did not now 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 call it in question.
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 that “God” owned him, and the people regarded him as a distinguished teacher.