How wonderful it is in such times to have a rock to lean on, or a high tower to flee to. How wonderful it is when our foot is slipping or our faith is sliding to know that there is something firm and immovable—something solid—that can shore us up and stabilize our uneasiness.
Elder Jeffrey R. Holland, "For Times of Trouble"
One of my favorite scriptures is Helaman 5:12. Helaman is imploring his sons to affix their lives on Christ. Set Him as the foundation. He is solid. He is immovable. He will never crack.
In our temporal world, we would never think to build a structure without first establishing a foundation. A solid foundation where construction can begin on top of it. It would just be foolish to, one, build a structure on top of dirt. Dirt that shifts, moves, disintegrates when wet, and is full of air pockets. And, two, it would also be foolish to start building the roof first, then the walls, and then the floor.
Likewise in the spiritual realm... we should start with our foundation. Once the foundation is solid, start construction. We wouldn't start from the top down. That just doesn't make sense.
What's interesting to note is that our foundation is constantly becoming stronger or weaker, depending on the care and focus we give it. So, our structure will either stand up to anything that comes, anything thrown at it, or, it will fall because the foundation weakened.