The ancients said:

“It is easy for a worldly man to win Buddhahood,
(But) hard indeed is it to bring wrong thinking to an end.”
We can say, the practice is easy. We just have to overcome delusion to be Enlightened. Once we can overcome our delusion, then we will be free and Enlightened, like the Buddhas and Bodhisattvas.

Master Lien Ch’ih said:

“It is easy to be caught up in the causes of pollution,
(But) to earn truth producing karma is most hard.
If you cannot see behind what can be seen,
Differentiated are (concurrent) causes,
(Around you) are but objects which, like gusts of wind,
Destroy the crop of merits (you have sown).
The passions of the mind e’er burst in flames,
Destroying seeds of Bodhi (in the heart).
If recollection of the truth be as (intense as) passion,
Buddhahood will quickly be attained.
If you treat others as you treat the self;
All will be settled (to your satisfaction).
If self is not right and others are not wrong,
Lords and their servants will respect each other.
If the Buddha-dharma’s constantly before one,
From all passions this is liberation.”

The pollution in this quote represents our delusions. Our vision is obscured by our delusions and desires.
If we strive to awaken with the mind of Enlightenment, then we can get through this delusion and see the true nature of things.

The Sixth Patriarch said:

“Although their faults are theirs and are not ours, should we discriminate, we too are wrong.”
Discrimination is the way we cling to things. “I need this to happen to be happy.” is a dangerous thought to have. But if we serve others and we don’t discriminate, then we can spread seeds of Awakening, like the Buddhas and Bodhisattvas.
The famous Ch’an teacher Upasaka Pang wrote this poem:
There is neither ego nor personality,
Who is distant then and who is intimate?
Take my advice and quit your task of comment
Since that cannot compare with the direct quest of the truth.
The nature of the Diamond Wisdom
Contains no foreign dust.
The words “I hear”, “I believe” and “I receive”
Are meaningless and used expediently.”

In this he was saying we shouldn’t discriminate to our discursive thinking.