One needful thing is to know by revelation from God that Joseph Smith was truly His prophet of the restoration, that Joseph saw God and Jesus and that through him the fullness of the gospel was restored to the earth.
Once God has confirmed that absolute truth, that needful thing, to our souls by His pure and holy spirit, it becomes a rock of defense. Then when salamander forgeries, slanderous news reports, fraudulent journals, deceptions of Satan, or flawed human discoveries, assail us, we can rest secure in the knowledge that no man-made, flesh-based, human-centric thing, can destroy the revelations of God. We need not spend hours trying to discover if Joseph really looked into a hat to interpret the Book of Mormon. We can reject outright any scandalous journal entries or claims by fame seeking contemporaries of Joseph that cast doubt upon his virtue or morality. We can remain unmoved by scientifically declared “authentic” letters and writings of the prophet which contradict the revealed truth, knowing that one day they, like the salamander letter, will be proven a fraud. In short, we can stop fretting over rust and stale crackers, and rejoice in our salvation, and the unmoving absolute truths God reveals. All the lesser thing will in that way remain interesting only, but never become controlling.
It is important to note that Martha was apparently NOT troubled about many things for her own selfish desires. It appears her motivations were good and others centered. Yet they still kept her apart from the needful things. Similarly, we may be lead into the endless monotony of trivial things, because we are seeking answers to help others who only know the flesh. We may, because we love those we find lost in a the flesh reliant world of minutia, move into that world and try to find the right minutia for them, in order to try and save them. However, the fact remains that they will never be saved by minutia, no matter how long we dwell on it, or how compelling we make it seem, they do not need to be convinced by flesh, they need to be converted by spirit. Such conversion is the truly needful thing.
Later in the talk by Elder and Sister Renland, Elder Renland told of an associate who had doubts about the Prophet Joseph Smith, based on the varied accounts of the first vision. He was referred to an expert in church history on that point. When Elder Renland saw the man again, he asked how he was doing. The man replied: “fine, I do not have any questions about that anymore, but now my question is about polygamy." Again, he was referred to a different historian with expertise in that area. When asked later how he was doing, he mentioned that his questions about polygamy were answered, but that he was then troubled about race and the priesthood….The man eventually fully apostatized.
The problem was not the man’s questions, sincere truth seeking is good and noble. His problem was the sources to which he looked to find his answers and his inability to look deeper and seek to know truth on the core issue, the needful thing, which was the divine calling of the Prophet Joseph Smith. Instead of praying for a spiritual witness from God to the truth about Joseph Smith, he was inundated with flesh-based reasoning and arguments presented by well meaning experts which did to some level satisfy his fleshy reason, at least on the particular troubling triviality, but which did not, in fact could not, get to the rock of the matter, and so he searched on, through one set of minutia to another…ever learning, but never able to come to a knowledge of the truth. Had he set aside the flesh, and focused on the spirit, his search would have been fruitful, the deep truth with regard to Joseph Smith, once gained, would have been life changing for him, and his many lesser questions would have become mere points of interest, not causes for apostasy.
Of course to accept God's revelations as being vastly superior to our human reason, requires us to understand the truth of the relationship between God and man, to recognize and accept the supremacy of His thoughts and ways to our own. It requires the third key to avoiding personal apostasy.......Humility.