In many respects Chan/Zen can be looked upon as a preliminary path which is done in preparation for the attainment of kenshō 見性 which is the intuition of our true nature. Zen is somewhat like military bootcamp which is a process of making the average person into a good soldier so they will be able to defend their homeland. Zen is demanding like in the military but somewhat different insofar as it spends a great deal of time on the inner territory of the person and their mental activity. Then, at some point the adept has to make a clearcut breakthrough, attaining the state of Buddhahood (buddhatā).
To sum it up, Zen is more about making us into good practitioners who will be able, eventually, to intuit their true nature which is the same as nirvana, including many other names such as the One Mind, true Mind or pure Mind to name just a few. Zen in this regard is not the end but more about learning the means that will be used to reach the end.
The preliminary quality of Zen is best found in Jeffrey L. Broughton’s translation of Whip for Spurring Students Onward Through the Chan Barrier Checkpoints (Changuan cejin), which he published under the title, The Chan Whip Anthology: A Companion to Zen Practice. Zen, that is, preliminary Zen, has its entire practice (gongfu) focused on intuiting our true nature (見性) which is the fundamental basis of reality.
So now let's imagine someone has made a breakthrough and reached kenshō, then what? Is their anything after enlightenment, in other words? Well, yes there is—a huge amount. This is from Treasury of the Eye of Truth Teaching Volume II by Thomas Cleary:
At that time a monk asked, “Is there any further cultivation for someone who is suddenly enlightened?”
Guishan said, “If one has truly realized the fundamental, that is when one knows for oneself. Cultivation and no cultivation are a dualism. Now though a beginner attain total sudden realization of inherent truth from conditions, there is still the habit energy [vāsanā] of beginningless ages which one cannot clear away all at once. It is necessary to teach that person to clean away the currently active streaming consciousness. This is cultivation, but it doesn’t mean there is a special doctrine to teach one to practice or aim for. Gaining access to truth from hearing, when the truth heard is profound, the immaculate mind is inherently complete and illumined, and does not abide in the realm of delusion. Even if there are a hundred thousand subtle meanings according to the times, this is getting a seat, wearing clothes, and knowing how to live on your own. Essentially speaking, the nominal ground of reality does not admit a single particle, while the ways of Buddhist service do not abandon a single method. If you enter directly at a single stroke, then the sense of ordinary and holy ends, the substance of being is revealed, real and eternal; noumenon and phenomena are not separate. This is the Buddha of thusness as such.
What is really happening is the adept, who has just had kenshō, is now like a baby lion that needs to grow up (the Bodhisattva's path). He or she will go through many, many samadhis overcoming their habit energy as the luminosity becomes progressively stronger reaching a point when the everyday world the adept inhabits becomes completely filled with this mysterious luminosity.