The dirt which usually does not go with water is actually orgaic in nature. So it can only dissolve in an organic solution. Soaps contain organic material which when dissolved in water forms a solution. When this solution is used with the clothes, the dirt dissolves in the soap solution and forms small droplet like structures called as micelles. These micelles remain suspended in water and hence the dirt is removed efficiently from the clothes. This is the cleansing mechanism of soaps.