Natural soap is handmade the old fashion way, using all natural ingredients. Store bought soap is mostly synthetic, and is full of harsh detergents and chemicals. Most large-scale manufacturers of soap extract glycerin from soap and sell it as a by-product to other companies.
In fact, most store bought soap you are using right now is a detergent bar, not soap. If you get out of the shower and your skin feels tight and itchy, there is a good chance you are using detergent on your skin.
On the other hand, using organic, natural, handmade soap, is the perfect way to actually achieve that skin 'to die for'. As it contains only natural ingredients, there is no chance of developing any allergic reactions or other skin problems.