There is an incident recorded in Matthew, Mark, and Luke where Jesus was asked by the religious authorities in Israel, “By what authority do you do these things?”
Mat 21:23 And when he was come into the temple, the chief priests and the elders of the people came unto him as he was teaching, and said, By what authority doest thou these things? and who gave thee this authority?
Mat 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.
Mat 21:25 The baptism of John, whence was it? from heaven, or of men? And they reasoned with themselves, saying, If we shall say, From heaven; he will say unto us, Why did ye not then believe him?
Mat 21:26 But if we shall say, Of men; we fear the people; for all hold John as a prophet.
Mat 21:27 And they answered Jesus, and said, We cannot tell. And he said unto them, Neither tell I you by what authority I do these things.
Sometimes in the past, I have been asked this very question: “What gives you the authority to try to teach us?” in discussions on the Internet.
Some religious groups, denominations, churches, and perhaps individuals make the claim that they are the authority when it comes to correctly interpreting the Bible.
The same group of individuals who asked me “What gives you the authority to try to teach us?” also asked the very important question, “Where in the Bible does it teach we must go by the Bible alone?”
I answered, “It is very clear that the Bible teaches we must go by what the Bible alone teaches in Isaiah 8:20 and its immediate and related contexts.”
This verse can be better understood if we read it in more than one Bible translation:
Isa 8:20 To the law and to the testimony: if they speak not according to this word, it is because there is no light in them. (KJV, King James Version)
Isa 8:20 To the law rather, and to the testimony. And if they speak not according to this word, they shall not have the morning light. (DRB, Douay-Rheims Bible)
Isaiah 8:16-20 (Now to guard the prophetic record close, now to seal up these instructions, in the keeping of my disciples! What though the Lord hide his face from the men of Israel? To him I will look, and wait patiently for him; here stand I, and these children the Lord has given me, a portent, a warning sent to Israel by the Lord of hosts, who dwells on mount Sion. Men will bid you consult wizard and diviner, that talk in ghostly voices over their enchantments; Who doubts, they say, God will send his own people answer, an oracle from the dead to the living? By these instructions rather abide, this record of prophecy; who follows other inspiration, shall not see the dawn.) Ronald Knox translation
Isa 8:20 Then you must recall the LORD’s instructions and the prophetic testimony of what would happen. Certainly they say such things because their minds are spiritually darkened. (NET Bible)
The question of what standard we go by to determine the truth is very important.