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.