Luke 20:1-6

Luke 20:1 (KJB)
And it came to pass, that on one of those days, as he taught the people in the temple, and preached the gospel, the chief priests and the scribes came upon him with the elders,

Then after Jesus had finished teaching He had gone back into the temple and a delegation from the Sanhedrin had met Him there. In reference to the cleansing of the Temple by tossing out the moneychangers and those who bought and sold, they had approached Him with two questions. I am sure when they saw Jesus approaching the temple they had become a little nervous in anticipating another episode. This may have not been the full Sanhedrin which came to meet Jesus at the temple but no doubt representatives. Jesus was teaching and preaching at the time He was approached.

Luke 20:2 (KJB)
And spake unto him, saying, Tell us, by what authority doest thou these things? or who is he that gave thee this authority?

The first question was, “By what authority doest thou these things?” This question had challenged the nature of the authority of Jesus such as are you a Scribe? A Prophet? Or do you hold some other office? They wanted to know, based upon what did He do this thing? Then the second question, “and who gave thee this authority to do these things?” They wanted to know who gave Him the authority to come into the temple and to do those things? For the last three years, Jesus had been teaching that His authority had come from God but the Jewish leaders had chosen not to recognize this, as some accused Him of having a devil, and even His miracles had not convinced them. Their minds were closed to truth and would not be opened.

Luke 20:3 (KJB)
And he answered and said unto them, I will also ask you one thing; and answer me:

To answer a question with a question was the typical way of the rabbinical debate method. Many times the counter question would reveal the actual issue behind the first question, as it will here. Jesus will be glad to tell them by what authority He has done these things and who gave Him this authority if they would just answer one question for Him.

Luke 20:4 (KJB)
The baptism of John, was it from heaven, or of men?

Then Jesus asks them the one question which will literally box them in. He focuses them back on the baptism of John. Was it something ordained of Heaven or was it something designed by men?

Luke 20:5 (KJB)
And they reasoned with themselves, saying, If we shall say, From heaven; he will say, Why then believed ye him not?

Then the religious leaders went into conference and began to discuss it thoroughly. They may not have liked Jesus at all, but He did ask questions which would make them think and they knew they had to answer correctly or He would have them cornered again. They knew that if they responded that the baptism of John was from Heaven, then they would be asked why they did not believe it? It would make them look like unbelievers in front of all the people and that would cause them problems.

Luke 20:6 (KJB)
But and if we say, Of men; all the people will stone us: for they be persuaded that John was a prophet.

Then they discussed the other side of the question and that was if they told Jesus that the baptism of John was of men, then the people might stone them because the people held John to be a prophet. So it was the kind of question they would not be able to answer because either way, they were caught by their own unbelief.