Well, I don’t know. But after some thought, I have some ideas of why, at least, I’m grateful that they are.
First, let me differentiate between ordinances and covenants. Covenants are the promises we make with Heavenly Father, they’re sacred compacts, or agreements wherein we promise to do certain things in return for certain promised blessings.
Ordinances are the sacred ceremonies that often accompany such covenants, and I’ve frequently marveled at why there would be a physical component to these crucial acts. After all, if God knows our hearts and minds, why couldn’t we simply agree silently, or mentally? Why, for instance, be physically baptized to demonstrate our acceptance of the Savior? Why eat bread and water to remember him?
I have found that the physical component of an ordinance helps bring solidarity, and substance to what would otherwise be merely intellectual and conceptual. They physical aspect of an ordinance somehow makes the covenant to which it is associated more tangible.
As it is, the ordinance becomes a physical embodiment of the principles and promises we make in our covenants. It’s an act of substance demonstrating our desire, rather than simply some mental milestone.
It allows for much stronger symbolism, which helps the human mind more completely grasp and appreciate the meaning and reality of these commitments.
Covenants are usually made at crucial times during the process of progression towards exaltation, and these accompanying physical components add a more memorable encapsulation of the teachings principles leading up to that point.
In short, we are physical beings. We sacrificed and risked much to gain this mortality, and as such, may we more fully appreciate the opportunity to physically express our commitment to our Father who gave us these beautiful bodies.