Albert Barnes Commentary Mark 11:18

"And the chief priests and the scribes heard it, and sought how they might destroy him: for they feared him, for all the multitude was astonished at his teaching." — Mark 11:18 (ASV)

All the people was astonished. He became popular among them. The Pharisees saw that their authority was lessened, or destroyed. They were therefore envious of him, and sought his life.

His doctrine. His teaching. He taught with power and authority so great that the multitudes were awed, and were constrained to obey.