Luke 20:2
And spake unto him, saying, Tell us, by what authority doest thou these things? or who is he that gave thee this authority? And spake unto him, saying, Tell us, by what authority doest thou these things? or who is he that gave thee this authority?
The demand comes from the temple leaders — the chief priests and elders, the priests and rulers — who confront Him to know by what authority He acts and teaches and who gave Him that authority. Their challenge follows His cleansing of the temple, where He commanded the traders to leave and drove them out. Though He has a humble appearance and no earthly rank, He speaks with kingly authority that they feel but refuse to acknowledge. By confronting the corrupt priesthood He gives the people evidence of His divine mission and kingship, though reform of that priesthood will fail.
They press Him although they already have unmistakable evidence of His authority and Messiahship in many works, including the cleansing of the temple and His healings. They do not want evidence. Their challenge grows from pride, jealousy, and hatred after His rebuke. They hope He will claim authority from God and declare Himself the Messiah so they can deny it, twist His words against Him, weaken His influence, condemn Him, and put Him to death.
He answers by making His answer depend on theirs, asking whether John's baptism came from heaven or from men, from God or from human authority. They face a dilemma because John testified that Jesus is the Messiah, so acknowledging that John was sent by God with a divine mission would expose their failure to believe his testimony and require them to recognize Jesus. Denying it would anger the people, whom they fear. They evade the question and refuse to answer from cowardice, indecision, fear of the people, and unwillingness to accept John's mission. He therefore refuses to tell them by what authority He acts, and their evasive answer leaves them confused and diminished and costs them the people's respect.