Using different interpretations of certain biblical verses, most of Christianity has been fairly confused as to the role of choices in salvation. Choice is usually associated with works, and works are usually seen as the opposite of grace. Those who emphasize grace usually de-emphasize works and choices.
The revelations of God to the Latter-day Saints, mostly through Joseph Smith, make this doctrine much clearer. In essence, we are saved by choosing the love and grace of Jesus Christ, which leads to the desire to do good works. Because our good works will never be enough to qualify for salvation on our own, the grace of Jesus Christ will make up the difference. Choosing the grace of Jesus Christ takes work, but that work is only useful as long as it is leading to Him.
Most Mormons understand this. However, this ability to choose Jesus Christ or reject Him is sometimes overextended to an unequivocal belief in absolute free will. Here is what the Book of Mormon says about free will, or "agency:" "Wherefore, men are free according to the flesh; and call things are given them which are expedient unto man. And they are free to choose liberty and eternal life, through the great Mediator of all men, or to choose captivity and death, according to the captivity and power of the devil; for he seeketh that all men might be miserable like unto himself" (2 Ne. 2:27).
This scripture specifies that all people are free to choose Jesus Christ or not. However, this freedom is "according to the flesh." What does that mean?
First of all, we can all think of times when we are hungry, stressed, sleep-deprived, or otherwise limited. We may become withdrawn, thoughtless, or irritable. In these times, our agency is limited in two ways. First, it is harder to be kind, thoughtful, controlled, or disciplined. Second of all, it may sometimes be impossible to do those same things.
This never relieves us of responsibility to those we may have harmed. Instead, it gives us a responsibility to increase our agency by living the gospel (Allen Bergin said this once). The Lord once told someone that He commanded them to sell their farm so that they would not be tempted above that which we can bear. Likewise, He has commanded all of us to "retire to thy bed early, that ye may not be weary" (D&C 88:124).
The same is true of mental illnesses. The Lord will judge us according to our weakness, but we have the responsibility to do all we can to manage it wisely.
And where does the power and motivation come to increase our agency through wisdom? It comes from our love for Jesus Christ. "We love Him, because He first loved us" (1 John 4:19). We need Him. As Qui-Gon Jinn said, our focus determines our reality. As President David O. McKay said, what we think of Christ will determine who we are.
If we turn our eyes to the tree of life, which is the love of God as manifested in the condescension of Christ, then we will have the power to hold to the iron rod. We will have greater emotional and spiritual freedom to serve, to work, and to learn.