It never ceases to amaze me how powerful, and yet how fragile faith is. It is a power that can literally move mountains, its strength can lift us up to a better way, and it's fruit can be the most delicious and powerful source for overcoming any trial. But... like a weak, baby tree, it needs to be protected. Fed. Cared for. If it's not, it will break. Die. And then be thrown away. And who will throw it away? The very person who planted it. How is it possible that something once so cherished and strong can become so weak and unwanted, to the point where one completely dismisses its strengthening properties and forgets why they chose to plant it in the first place? How is this possible? Why doesn't faith strengthen and renew itself? How can something so strong, spiritual and powerful, just die?
Answer: Because faith is only a power if it is being used. It's not real unless someone chooses to make it real. Because it is not a physical, tangible force, it relies upon human touch in order for it to activate, and hence, thrive. The human source must continually strive to strengthen the spiritual power in order for it to be of use. "Faith without works is dead, being alone" (from James 2:17). This is a literal truth. Actual faith, it's power and essence, will no longer exist where someone is not using it. And without the human host, it is alone, and faith cannot survive on its own. Just like a baby tree as Alma said.
Now, one might argue that there are plenty of thriving trees in the world that have grown without human contact and therefore it's arguable that faith should be able to flourish and maintain itself without having to put in so much personal effort. But these trees, since their birth, have been nourished by God himself, their creator, the physical being who planted them. But he cannot plant and maintain a tree for us. We can appreciate His faith and the strength it brings to others and ourselves and partake of its fruit, but unless we plant our own faith and nourish it ourselves, we will never understand nor experience the full strength and power of flourishing, nourishing faith. How important it is to make the daily effort to strengthen our faith! Without us to strengthen and nourish it, it will literally die, for it just cannot survive alone. It is so powerful, and so fragile all at the same time. And we are its greatest source of strength.