It is able to wash all earthly skin, including the skin of man. Its effect is enormous, its service invaluable. But it cannot wash away the greasy impurity of the human soul. But the water was never able to touch the impurity of their soul. And internal impurity accumulated in them to such an extent that, once it was vented and poured out on the most pure Lord Jesus, its stench has been spreading itself all over the world even to the present day.
Water is just a symbol.
Physical washing is a symbol of spiritual washing. A symbol can wash a symbol, but not reality. Water can wash the exterior face of man, but not his interior face. And this interior face of man is the image of God in man-the living soul with the spiritual reality within it. Therefore, only God alone, through the power of His Spirit, can wash away the spiritual impurity in man.