What is the meaning of “Constantly guard the six doors and

don’t let the soul pass by” in Scriptures?

The Six Doors are the eyes, ears, nose, tongue, body and mind. 

If these doors are not guarded, one’s will wanders in and out through

them; so not only a practitioner of Tao will never attain Tao, he might

even return to the cycle of birth, death and rebirth upon his death.  Why? 

The eyes, ears, nose and tongue are doors leading to rebirth as four kinds

of animals, and are also known as the four paths of birth.

If one desires for sights excessively, his soul will leave the body through

the eyes upon death.  He is destined to be born again as birds for others to

watch and enjoy.  If one listens to heresies excessively, his soul will leave

the body through the ears.  He is destined to be born again as

domesticated animals for others to order.  If one desires for aroma

excessively, his soul will leave the body through the nose.  He is destined

to be born again as insects to taste all filth and bad odours and will die of

sucking and biting their victims.  If one likes to slander others or criticize

others, his soul will leave the body through the mouth.  He is destined to

be born again as aquatic lives.  This is because the mouth is symbolized

by kan in the eight trigrams, which also symbolizes water or scales.

For those who practice heresies, do not practice filial devotion, and

perform wicked deeds, they will be punished in future lives.  This is

the eternal law of karma.  For those few who practice their virtues

and perform good deeds but are not meant to encounter Tien-Tao

during their lifetime, they will be rewarded in their future lives by

being born in rich, powerful or influential families, enjoying wealth,

power or fame.  Once their rewards are exhausted, their souls still

return to the Underworld.  These are the six paths in the cycle of birth,

death and rebirth.

Realizing the consequences of the six paths, Lao-tzu taught others to

constantly guard these six doors to avoid souls passing through them. 

The five external doors – the eyes, ears, nose, tongue and body – are

relatively easy to guard; however, the internal door – the mind – is

difficult to guard.  The mind, resides in the spleen, is called Yin-shen

(the yin spiritual image).  To tackle this, Taoism devised a dumb

technique: concentrating one’s mind at the Right Portal constantly. 

This method lets the True Fire of old yang (the aureole) refine Yin-shen. 

If one practices this technique continuously as if he is retarded or slow,

he can attain a calm mind and have clear wisdom after a hundred days. 

With prolonged practice, one will act according to his True Nature and

need not guard his Six Doors anymore.