"And the king said: How knowest thou the thoughts of my heart? Thou mayest speak boldly, and tell me concerning these things; and also tell me by what power ye slew and smote off the arms of my brethren that scattered my flocks-
"And now, if thou wilt tell me concerning these things, whatsoever thou desirest I will give unto thee; and if it were needed, I would guard thee with my armies; but I know that thou art more powerful than all they; nevertheless, whatsoever thou desirest of me I will grant it unto thee." (Alma 18:20-21)
King Lamoni was willing to pay a handsome price to learn the knowledge, even to half his kingdom. But knowledge without change is of little benefit. In other words, King Lamoni wanted knowledge but didn't want to pay the price for it. Ammon detected the lack of willingness to change in the king's question and so rather than jumping in to the gospel he first gained a commitment from the king that he would not only be a hearer of the word but also a doer of the word (James 1:22).
"Now Ammon being wise, yet harmless, he said unto Lamoni: Wilt thou hearken unto my words, if I tell thee by what power I do these things? And this is the thing that I desire of thee." (Alma 18:22)
The word "hearken" involves acting on that which is received, not merely accepting it.
"And the king answered him, and said: Yea, I will believe all thy words. And thus he was caught with guile." (Alma 18:23)
"Guile" means deception. It was deception for the king to show sincere intent in asking a question when he had no intention to do anything when the answer was given. Notice that Ammon asked if he would hearken to his words and the king replied that he would believe his words. The true definition of "believe" incorporates acting upon the knowledge. At first the king had no intention to act upon the knowledge but now he stated that he would by using the word "believe". A king cannot go back on his word thus such a commitment was no small ordeal!
This is an example of how the usage of the word "believe" as used today is not the same as used in the scriptures. Today we often use "believe" when we really mean "accept". When we read the word "believe" in the scriptures it should be with the understanding that we not only accept what is being stated but that we will also do something with that knowledge.
Sadliers, Avow, 2016