“Hmmmm . . . always wondered about that expression. I think I know what it means, but how did it come about?”
What does it mean?
“That something is given the test that proves it genuine or not.”
“Well, how about it?”
In times when gold coins were in circulation, nitric acid was applied to a coin. If it deteriorated, it was false; if no harm came to it, it was deemed genuine. Do you know what is the acid test for whether or not one is a true Bible teacher?
“No. What is it?”
John says, “We are of [from] God. Whoever knows God listens to us, but whoever isn’t of [from] God doesn’t listen to us. From this we know the spirit of truth and the spirit of error” (I John 4: 6). All else will corrupt!
The acid test, in the New Testament is the same as in the old—whether or not one listens to God’s Word. The apostles were given the task of proclaiming that Word inerrantly. So, we measure the truth of one’s teaching by how closely it conforms to the Scriptures (the apostolic Word).
“Then, we don’t look for signs, or wonders, but only how close one’s teaching is to the Bible?”
You got it. See Deuteronomy 13 where we are warned about following signs and wonders. That will help as well.