4 And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost.
Basically, it’s saying if you do A, you will get B result. I’m not saying I know everything God has to teach us, so of course I’m willing to pray and ask Him to show me if the Book of Mormon is true. So I prayed about it, but nothing happened. Multiple Mormons have said I just need to keep reading and praying about it.
But there’s a big problem with that thought process. Do a Google search on ‘placebo effect’ and you’ll see how powerful the human mind can be when it expects something to happen.
"Research on the placebo effect has focused on the relationship of mind and body. One of the most common theories is that the placebo effect is due to a person's expectations. If a person expects a pill to do something, then it's possible that the body's own chemistry can cause effects similar to what a medication might have caused.
For instance, in one study, people were given a placebo and told it was a stimulant. After taking the pill, their pulse rate sped up, their blood pressure increased, and their reaction speeds improved. When people were given the same pill and told it was to help them get to sleep, they experienced the opposite effects.
Experts also say that there is a relationship between how strongly a person expects to have results and whether or not results occur. The stronger the feeling, the more likely it is that a person will experience positive effects. There may be a profound effect due to the interaction between a patient and health care provider."
Notice the second bolded part and compare it with the 'sincere heart' phrase in the verse. So if an investigator prays and doesn't receive a witness the first time, they are encouraged to keep reading and try again with a sincere heart. But trying harder just makes a stronger placebo effect more likely.
In a recent, well-publicized and fascinating study of Parkinson disease (PD), it was discovered that the patients who improved with placebo had changes in their brain that were identical to the changes caused by the actual medication (called levodopa).
The placebo effect can go far beyond emotional reactions. Their brains changed themselves simply because they expected it to happen.
That's just from the first page of Google results. I'm sure I could find many more examples. The human mind has an incredibly powerful ability to create reactions, changes and/or events when we expect them to happen.
Like I said above, I’m not opposed to God revealing some new truth to me. A common response from a Mormon is that we just need to have faith that God will reveal the truth to us. But God already has revealed truth to us through the Bible. Relying on prayer like they suggest is putting a lot of faith in the human ability to discern between a response from God and a reaction generated by our expectations. Continuing to pray about it while expecting a response is also putting an extreme amount of faith in the Book of Mormon and Joseph Smith before you receive confirmation from God.