Consider the following account recorded in the Doctrine and Covenants, section 67. The occasion was a priesthood gathering in Ohio where the brethren were discussing what to do with the written revelations received through Joseph Smith. It was decided at that meeting that the written revelations should be published.
I imagine that the written records were laid out on a table before them as they discussed what should be done. Some of the brethren testified that the records were true and that they had received this witness through the power of the Holy Ghost. Others, however, debating the language contained in some of the revelations. They thought that if this or that statement had truly come from God, it would have been worded differently. Perhaps these individuals wanted to “wordsmith” some of the text so that it agreed with what they think the Lord might have said. Or maybe they wanted to strike some text from the records thinking that it came from the prophet's own thoughts.
I can imagine the prophet sitting there dumbfounded by the skepticism that had crept into their meeting. He might have testified to the skeptics that the revelations came directly from the Lord. What is certain is that during the meeting, the voice of the Lord came to those men through the prophet and testified that the revelations were genuine. But the Lord did not just command them to believe, He reasoned with them.
In verse 6 the Lord challenges the men to find the least (simplest) revelation contained in the manuscript. Then He tells them to pick the wisest (most learned) person from among them. If that wise person can create a revelation “like unto” the least revelation, then they “are justified in saying that ye do not know that they are true.” But if the wisest person cannot create a similar revelation, then they can know that the revelations came “down from above, from the Father.”
I don’t think that any of the brethren actually carried out this experiment. More than likely it was meant to be a thought experiment, or a gedanken experiment, as it is sometimes called. A thought experiment is an experiment that is carried out in one's mind. The Lord gave them a thought experiment knowing that it can be a very powerful source of truth. When the brethren imagined the outcome of the Lord’s experiment, they knew in their minds what the outcome would be.
(Interestingly most of Einstein’s discoveries came through thought experiments. Only recently has science carried out actual experiments [here and here] that confirm Einstein’s ideas.)
Human reason, when exercised correctly, has the power to convince people of spiritual truths. Everyday our missionaries open the scriptures and reason with people around the world. They reason with people about the existence of God and the reality of the Restoration. Those who accept the missionaries’ reasoning, humble themselves and pray for an answer, receive a witness through the Holy Spirit.
Human reason leads not just to secular truth, but spiritual truth as well. When we ponder things in the spirit of righteousness, the Spirit guides our thinking and leads us to knowledge.