Question

if soap and water clean the body then what makes towel dirty

Answer 1

After washing your body with soap and water the dirty water still remains on your body. You use the towel to rub that dirty water. This makes the towel dirty.

Answer 2

Soap and water do not clean dirt from the body.

Soap, water and abrasion do.

And they only do it a single layer at a time.

Much “dirt” is actually entrenched in the pores of the surface skin, and that skin is only partially sloughed off with soap, water and a cloth, sponge or loofah.