It's analogous to your own health. If you survive on a diet of junk food and pills, you won't be nearly as healthy as someone who eats whole grains, fresh fruits and fresh vegetables. Your body needs the different nutrients, fibers, vitamins and minerals found in fresh whole foods, but lacking in pills. Similarly, your plants need the nutrients, fungi, bacteria, minerals and trace elements found in healthy soil, but lacking in a bag of green crystals. Lets start with what exactly is soil.
Most people think of soil as ground up rocks.
But soil is much much more. It's a complex ecosystem that depends on a balance of water, air, organic mater and minerals. Minerals are those tiny pieces of rock that most of us think of as dirt. To hear most gardeners talk, the only size particle found on earth is clay. Clay is not all bad.