By profession, I am a toxicologist, specializing in soils. First I was an soils scientist and then specialized in toxicological issues with soils. So, at the root of it all, soil is my first passion.
First off, soil is not dirt. Soil is a living, breathing organic matter. Dirt is something you get under your nails. There are many components to soil; organic matter, color, composition, pH, etc. Dirt is what causes the stains in the knees of freshly washed pants.
Soil is what grows the bounty of our planet. Dirt is what is tracked in the house on the souls of shoes.
If you are going to successfully garden, you must have an understanding of soil. Sure you can throw seeds into the ground and grow a garden. It may even be a great garden. But if you keep managing your soil without an understanding of soils' needs, it will only be a couple of years before you have depleted the soil of the essential nutrients needed to maintain a healthy balance within your soil.
Microscopically, the soil is teeming with beneficial bacteria.