This challenge to Jesus from the chief priests and elders, was NOT founded in any honest desire to submit to His authority! Rather, it is obvious that they were seeking occasion to reject Him.

Of course He was not there by authority from the chief priests, or the elders. They could easily refute that. And if He claimed authority from God, they were more than ready to dispute that!

So His reply was a question which challenged their own authority to question His authority.

If they could accept that John was a prophet from God, then they would already know that His own authority to teach, (and the teaching itself) came from God, and NOT from men.

On the other hand, if they thought that John was just another self proclaimed prophet, acting on his own initiative with no authority from God, then they could also reject John's endorsement of Jesus as the Messiah.

And if they did not have to accept what John said about Jesus, then neither need they accept it from Jesus.

Thus for Jesus, if they did not already know where the teaching came from, there was really no point at all in debating with them the question of whether or not He spoke with authority from God.

Jesus refused to defend His authority !

On another occasion, when the teaching became too hard for the "itching ears" of the crowds, " many of His disciples drew back and no longer went about with Him ". (John 6:66 RSV)

Jesus left it to the twelve to decide what they wanted to do. He said to them, " do you also wish to go away ?"

Simon Peter answered Him , "Lord, to whom shall we go? You have the words of eternal life; and we have believed and come to know, that you are the Holy One of God."

They knew where his words came from!

What is good for Jesus is also good for those who follow Him.

It may sometimes happen that we also are challenged as to our "authority" to speak for God, (or even to exist as a local church assembly). When it does happen, we need to do as Jesus Himself did. 

It is NOT to be argued with men! (Especially those who seek a reason to reject us) Indeed if we do defend our authority, we shall become just one more competing voice amongst the confusion of the many others, all making the same claim, and all saying different things !

The only worthwhile response to those who challenge our authority to speak for God, (or write for God), is to invite them to check out the truth of what is said, against what is written in the Bible.

They do not have to accept it from us !!

But if they do find that what we say is also what GOD says in His Book , then they can take the question up with Him as to whether they accept the authority of what He has inspired to be WRITTEN there!

Neither do I tell you by what authority I write this, or by what authority our Church exists !