Matthew 21:24
And Jesus answered and said unto them, I also will ask you one thing, which if ye tell me, I in like wise will tell you by what authority I do these things. And Jesus answered and said unto them, I also will ask you one thing, which if ye tell me, I in like wise will tell you by what authority I do these things.
Confronted by the chief priests, elders and rulers demanding by what authority He acted, Jesus answered with a question of His own, promising that if they told Him He would likewise tell them by what authority He did these things. His counter-question asked whether John's baptism came from heaven or from men, from heaven or from people, from God or from human authority. To admit it was from heaven would expose their inconsistency and require them to face why they had not believed John, to face his testimony about Jesus and his testimony identifying Jesus as the Messiah.
John had attested Jesus after His baptism as God's beloved Son and as the Lamb who takes away the sin of the world. To call John's baptism merely human, merely of men, would turn the people against them, because the people held John as a prophet, so they feared losing the people's support and facing the people's wrath and anger. They acted from self-interest and fear of the consequences of either reply rather than seeking truth, and would not say what they believed, choosing to feign ignorance and say they could not tell rather than admit what they had recognized and yield to their convictions and answer honestly.
His healing works had already given them undeniable evidence of His authority, and His words and works of love and power had revealed His moral supremacy, yet they refused to recognize God in Him and wanted a statement they could twist against Him. Their refusal exposed their unwillingness to accept the evidence despite John's God-given mission and divine mission. Those who would not heed John's warning would not heed Christ's words either, would not accept Jesus' words.
When they refused to answer, Jesus withheld the declaration of His authority and declined to tell them, leaving Himself free not to tell them by what authority He acted. Thereby He turned their snare back on them, silencing, baffling and defeating the proud, self-righteous questioners before the watching multitude. He challenged them to face the evidence of His divine mission and gained opportunity to set before them their true position with further warning, not to humiliate them or from gladness at their hard place but to teach an important lesson.