Why pray about the Book of Mormon and Joseph Smith

 I recently heard a great podcast by a wonderful man who brought up something that really brought some things to light. Why, if we know the Word of God, do we need to pray to receive an answer to something that contradicts the Bible (The word of God)?

His name is Mark Spence. He's had many conversations in his travels with many people of different faiths, as well as LDS Missionary Elders. When he gets into a discussion with Mormons, he tries to challenge them, their statement to him, that he needs to simply pray whether or not Joseph Smith is a Prophet and the Book of Mormon is the word of God.

He says "Should I really ever pray about Joseph Smith being a prophet? It doesn't seem like this is something I really should pray about. I just need to see if the things he said line up with scripture. Deuteronomy 18 says that if a false prophesy comes about, well, it's not a prophesy from God and he's not a prophet from God. I don't need to pray about whether the Book of Mormon is the word of God. I simply need to see if it lines up with  the text that has already been given to us. Gods inspired, infallible word."

Mark then makes the statement more practical for them. "Should we ever pray whether or not we should steal a ball point pen?
They then say, "No, you should pray about that."
Mark then adds, " Why not? Think about all the good I'm going to do with this pen. In fact, I'm going to designate this pen to only writing encouraging letters to Elders in the mission field. Or perhaps, I will use this pen to write checks to the local Mormon Ward. Those are the only two things I'm going to be doing with this ball point pen. So, should I pray whether or not I should steal this ball point pen?"
They say, "No, don't pray whether or not you should steal a ball point pen. That's ridiculous."
Mark says, "Why not?"
They say, "Because God has already told us that you shall not steal."
Mark says, "Exactly. Where has God told us we shouldn't steal?"
They Answer. "Exodus 20. Ye shall not steal."
Mark continues, "But, what if I steal this pen from a guy who owns a ball point pen factory? He's not going to miss it. Especially in light of the fact I'm going to tell him what I'm going to do with this pen. He would probably give it to me anyway. What do you think? Should I pray whether or not I should steal this ball point pen?"
The answer then is usually, "No. Don't pray."
"Why?"
"Because God has already told us not to steal."
Exactly! So why should I pray whether or not the Book of Mormon is the word of God or Joseph Smith is a Prophet? How is God going to answer me?
To which they say James 1:5. God's going to give us wisdom.
How's God going to give us this "Wisdom"? Ultimately, it gets down to an answer of 'You'll just know' also known as a 'Burning of the bosom'. They don't use that phraseology anymore as it's a dangerous territory. We don't need those sort of things. Gods word transcends time and we can test it. It's trust worthy. We just need to see whether or not it lines up with scripture. If it does, your good. If it doesn't, you need to throw it out.