Nothing bad will happen to you or your body if you don't wash your body using soap.
However getting clean without soap is a hard thing to do as soap helps to remove dirt and grime as well as sweat from your body.
You can just shower without soap and just shower with warm water and be somewhat clean but if you do not wash your body with soap then some dirt and grime as well as sweat can be leftover on your body.
That then can make you smell of body odor and sweat and other grime even if you yourself cannot smell it.
Other people can smell it so I would recommend at least washing with soap every other day.
But I prefer to wash my body using soap as I never felt clean enough when I tried washing my body with just water.
But if you do skip some days using soap then your skin may actually be healthier because soap has been known to dry out your skin and strip your skin of some essential oils.