For clarity of vision, the mind has to be cleansed of the five mental hindrances.

They are - 1. sensual lust, 2. ill-will, 3. sloth and torpor,

4. restlessness and worry, 5. doubt.

Freedom from these hindrances is basic for all levels of concentration and insight. Therefore one who wishes to attain the calm of concentration and the clarity of insight, has to go on purifying the mind from these hindrances.

In order to illustrate to the Brahmin Sangarava, how these hindrances impair calm and clarity of the mind, the Buddha once used the simile of a bowl of water.

If one wishes to use a bowl of water as a mirror to see one’s face in it, the water in the bowl has to be clear enough to reflect it. When some colour like red, yellow, blue or brown has already been mixed into the water, it will lack the clarity to mirror the face. Even so lust is a colouring agent in the case of the mind.

When the water in a bowl is boiling and bubbling, it can hardly reflect one’s face in it. The fire of ill-will keeps the mind boiling, hindering its reflective capacity.

A bowl of water covered with moss will never serve as a mirror. A mind inert and rowsy with sloth and torpor cannot reflect properly.

If a bowl of water is shaken by the wind so that the water is rippling, disturbed and unsteady, it will not be possible to see clearly one’s face in it. Restlessness and worry affect the mind in a similar way.

A bowl of muddy water placed in a dark corner lacks the property of reflection. A mind in the grip of doubt and wavering is likewise muddled and murky. It lacks the property of proper reflection.

When the mind is free from these five hindrances, memory, mindfulness, concentration, calm and insight come in unhindered. One sees things as they are in the mirror of the mind.