I was asked this recently when using several crystals in a Health Kinesiology session.
Crystals are part of the bedrock of this planet, deep within it, layered in time, evolution, development and knowledge of all that exists. Yes, all that exists, within us, all our experiences and all that is and is not of this planet we call Earth or Gaia.
So to answer the question; within crystal form is the vibrational resonance of aspects of ourselves, the whole us, the us as part of the Universe, of Earth, of each other.
Careful use of the right crystal unlocks or heals part of our core energetic memory, it helps release a block allowing us to move forward, to be more of our potential, to BE, to KNOW.
We are AMAZING. There is more to life than meets the eye.