Mark 11:28

And say unto him, By what authority doest thou these things? and who gave thee this authority to do these things?

The question was put to Jesus in the temple by the temple leaders — the chief priests and elders and rulers, the Sanhedrin — demanding by what authority He did these things and who gave Him that authority, for His actions and His teaching, and especially for taking charge of the temple, cleansing it, and driving them out. It came as He was teaching in the temple on the day after the cleansing. That cleansing was an exercise of His kingly office and part of His divine mission.

Those who challenged Him had fled before the command of a carpenter's son, a poor Galilean without earthly rank or power, because He spoke with the authority of a king and there was in His appearance and voice what they had no power to resist. At His word they saw themselves as hypocrites and robbers, and as divinity flashed through humanity they felt as if before the throne of the eternal Judge with their sentence passed for time and for eternity. For a time they were convinced He was a prophet, and many believed Him to be the Messiah, as the Holy Spirit brought the prophetic utterances concerning Christ to their minds.

They refused to repent and yield to that conviction because His sympathy for the poor exposed their extortion, because He discerned their thoughts they hated Him, because His public rebuke humiliated their pride, and because they were jealous of His growing influence with the people. He had already given them abundant and unmistakable evidence of His divine authority, Messiahship, and mission, yet they did not believe. In particular, His cleansing of the temple and His healing works were that unmistakable evidence of divine authority. In particular, His miracles and other evidences attested His Messiahship.

They were not seeking evidence but asking to trap Him and gain grounds to deny and condemn Him. They wanted Him to declare Himself the Messiah so they could twist His words against Him, turn the people against Him, destroy His influence, and put Him to death. In answer He asked them whether John's baptism was from heaven or from human authority.

The question exposed their dilemma, since accepting its divine origin would require accepting John's testimony to Jesus as the Lamb of God and Messiah and facing the truth about Jesus, while denying it would anger the people. Their evasive reply that they could not tell exposed their unwillingness to accept that testimony and led Him to refuse their question about His authority, leaving the rulers silenced and diminishing the people's respect for them.