Soap works by making water wetter than it already is. There's a kind of skin on water and if you can't break that skin, you can't get things wet. And you need to wet things to rinse away dirt.
Soap breaks the skin.
That helps it to rinse away greasy dirt. You Can do these two experiments to see how soap works. Look close at the edge. Use the teaspoon to add more water. You Can add more than you think.