Murky water is turbid, let it settle and it will clear, A dusty mirror is dim clean it and it is bright.
The Tao is clarifying the mind and perceiving its essence.
The reason peoples minds are not clear and their natures not stable is they are full of craving and emotion. Add to this the cons of mental habit, aquired influences deluding the mind, their outgrowths clogging up the opening of awareness - this is like water being murky, like a mirror being dusty. The original true mind and true essence are totally lost. The feeling and senses unruly, subject to all kinds of influences, taking in all sorts of things, defiling the mind.
If one can suddenly realize this and change directions, wash away polution and contamination, gradually remove a lifetime of biased mental habits, wandering thoughts and perverse actions, increasing in strength with persistence, refining away the dross until there is nothing more to be refined away, when the slag is gone the gold is pure. The original mind and fundemental essence will spontaneously appear in full, the light of wisdom will arise, and one will clearly see the universe as though it were in the palm of the hand.
Like murky water returning to clarity when settled, like a dusty mirror being restored to brightness when polished. That which is fundamental is as ever without any lack.