Our Mind-essence is originally perfect and bright. The reason that we cannot attain instantaneous enlightenment and partake of immediate enjoyment is the veiling of the Mind by the klesa of covetousnes, hatred, stupidity, and cupidity during the innumerable kalpas in the past. It is therefore necessary to practice gradual cultivation.
The Ch'an master Kuei-shan teaches that if a student can attain sudden enlightenment, he has only to apply his enlightenment to the purification of the manifested karmas and the flowing consciousness. This is called "cultivation." There is no other kind of cultivation.
If the student seeks only sudden enlightenment and stops there, thinking that there is no function or application, then the karmic force will go underground and erupt when conditions permit. Gradually, the mind will become a demonic realm.