"But this much I can tell you, that if ye do not watch yourselves, and your thoughts, and your words, and your deeds, and observe the commandments of God, and continue in the faith of what ye have heard concerning the coming of our Lord, even unto the end of your lives, ye must perish. And now, O man, remember, and perish not."
King Benjamin understood that what a person thinks about eventually leads to what he says and then what he does. If we want to keep our lives in harmony with God's commandments, the best place to start is with the things we think about. I know that I'm in trouble when I go to sleep thinking about how much I would rather sleep in instead of getting up to exercise. As soon as that thought takes hold in my mind, I'm doomed--the exercising never happens. But if I go to bed rehearsing to myself all of the reasons that I want to exercise in the morning, than I am more motivated to get up and do it. The power of our thoughts is amazing, but scary, too. The challenge is keeping control of our thoughts, instead of allowing them to control us.
I believe that this is one of the greatest benefits of fasting. By limiting our physical bodies, we are allowing our spirits to take control. We can either suffer through the day, miserable because of our lack of food and drink, or we can take charge, direct our thoughts to spiritual feasting and find ourselves wishing at the end of the day that the fast had lasted a little longer.
Remember the proverb: "For as he thinketh in his heart, so is he..." (Proverbs 23:7)