How are living organisms important for improving soil fertility

In healthy soil there is a whole ecosystem including bacteria, fungi and larger living organisms (like worms and grubs) that live in harmony with each other.  Like the human gut, soil needs beneficial microbes to function at its best. These organisms perform different functions that allow soil to breath, eat and cycle nutrients. Without these living organisms’ soil is biologically dead and anything that is planted will struggle to grow, not to mention be heavily reliant on fertiliser inputs, and be susceptible to disease and pests.