As the science of chemistry evolved, chemists began to understand , and explain, how soap cleans. Soap is made up of molecules with two distinct arms - a water bonding hydrophilic arm and a water rejecting hydrophobic arm. The hydrophilci arm bonds itself onto water molecule while the hydrophobic arm rejects the water and attaches itself onto dirt molecules.
So when you wash your hands and body, the water sweeps away the dirt molecules that has bonded with the hydrophobic arms of the soap.
That is why just washing with water does not clean the dirt. Just add some Midnight Oil, ALL NATURAL, Soap and you have a clean body that is dirt free!