People who meditate in the Chan Hall are actually taking a test. They are seeing whether or not they qualify for Buddhahood. How can they pass this test? Reach the state where, "Inside there is no body or mind, and outside there is no world."
It's a state of:

Looking, but not seeing;
Hearing, but not listening;
Smelling, but not noticing the scent.

Only a person who possesses this kind of skill can hope to pass the test.
Why is it described as "looking, but not seeing"? Because the person is "returning the light to shine within," and introspecting. Why is it "hearing, but not listening"? Because he is "turning the hearing back to listen to his own nature." Why does it say, "smelling, but not noticing the scent"? Because he has gathered back his body and mind, and is not disturbed any longer by scents. At this time, the cultivator's eyes contemplate physical forms, but the forms don't exist for him. His ears hear sounds, but the sounds don't exist for him. His nose smells scents, but those scents don't exist for him. His tongue tastes flavors, but for him, those flavors don't exist. His body feels sensations, but does not attach itself to those sensations. His mind knows of things (dharmas), but does not attach to them. Only when one reaches this kind of state does one have any hope of being chosen as a Buddha. Before you reach perfection, before you reach the highest summit, before you "climb to the very top of a hundred-foot pole, and take one further step," you have no hope at all of qualifying. Therefore, don't waste your precious time here in the meditation hall.

Ancient cultivators had a proverb that goes,

An instant of time is worth more than an ounce of gold.
You can't buy an instant of time with an ounce of gold.
An ounce of gold, if lost, can be easily replaced.
But once time has gone by, you can't bring it back again.

We must make the most of our opportunity to work hard and diligently cultivate. There are many ways to cultivate, but Chan meditation is surely the most lofty and supreme Dharma-door. When your efforts in cultivating this Dharma-door reach maturity, you'll be able to turn around, so that you "turn your back on the dust and unite with enlightenment," and get selected as a Buddha.

People who cultivate the Bodhisattva Path are able to renounce their external wealth, such as their countries, cities, wives, and children. They're also able to renounce their internal wealth, such as their heads, eyes, brains, and bone marrow. Bodhisattvas are able to give people anything they need; they are never stingy. A Bodhisattva's sole concern is to aid people; he doesn't calculate on his own behalf. Only one with this kind of attitude has hope of being chosen for Buddhahood here in the "Buddha-selecting field." Everyone should know that the selection is done by the Buddhas, and they are completely unbiased and impartial. No one can hope to attain Buddhahood by chance or luck. The only criterion is true spiritual skill.

Buddhas select other Buddhas; demons don't select Buddhas. Demons, however, do help Buddhas. Buddhas teach living beings in a direct manner, while demons teach living beings indirectly, from the reverse side of things. From the flip-side they exhort you on, giving you a chance to bring forth great resolutions and to apply yourself to serious cultivation. Demons thus count as Good and Wise Advisors in an indirect way.

I've often said:

Demons polish the True Way.
Only when the Way is true do the demons come.
The more they polish, the brighter you get.
The brighter you get, the more they polish you;
Polishing until you shine like the moon in space,
Which glows in the sky and
Sheds light on the hordes of demons.
When those hordes retreat before your light
Your fundamental Buddha-nature appears.

We needn't see demons as our adversaries. Treat them, rather, as our Good and Wise Advisors who aid us along the Way. If you can contemplate them from this viewpoint, then your mind will rest calm, and you'll be free of afflictions. People who slander us are really our Good and Wise Advisors. When we've performed correctly, but somebody finds fault with our job, then we should strive to further improve, and take one more step from atop the hundred-foot pole. "The person who finds my faults I will treat as my teacher." An individual who can point out our shortcomings is our teacher. We ought to show him gratitude and never feel antagonism or hostility towards him.

Buddhas would never be as muddled as we common people. If you always wear a phony mask to cover yourself, you'll never get selected to be a Buddha. You must be true within true, and truer than true. You have to be true, true, true, true, true, true, true! Seven times true! Then you can qualify. This is to be "seven times true and eight times correct" [an expression which means one must be thoroughly genuine and proper]. During the seven days of the Chan session, you genuinely cultivate, and on the eighth day you straighten out any crooked views. All bad habits and faults get swept away completely, and you are flawlessly pure, to the ultimate!