What is the use of practicing the mantra "Wu"?

Answers from Master Samael Aun Weor.

The Mantra WU is chanted with a double WOO, WOO, as if imitating a howling hurricane, amongst the boisterous waves of the furious sea. During this exercise, the mind must be absolutely quiet and in a profound and frightful silence (both in the exterior as well as in the interior); not even the slightest desire, nor the most insignificant thought must agitate the profound lake of the mind.

Samael Aun Weor.