Pure meditative concentration alone cannot give birth to wisdom

Question: When sitting in meditation, is it acceptable to empty oneself and single-mindedly keep watch on "emptiness"? 

Answer: Emptiness—how can you keep watch on it? That emptiness of yours is still a form of existence; this is like placing a head on top of a head. Dwelling in the state of emptiness, or sitting quietly with an empty mind, is pure meditative concentration (samādhi) and cannot give rise to wisdom. The Sixth Patriarch already refuted this very clearly in the Platform Sutra of the Sixth Patriarch. When reading, it all seems clear, but as soon as it comes to practical application, one becomes muddled. In samādhi, without contemplation of the Dharma principles, without contemplative practice (vipaśyanā-caryā), without questioning doubt, wisdom cannot arise. For example, in the samādhi of recollection of the Buddha (buddhānusmṛti), no matter how good or deep the concentration is, if there is no questioning doubt within it, no contemplative practice, no investigation, how could wisdom arise to eliminate self-view (ātma-dṛṣṭi) or to see one's true mind?

What is contemplative practice? Take worldly matters, for example: with some people and some matters, after experiencing them many times, one gradually sees through them and thereafter no longer cares about them. Contemplative practice is the same—after observing much, one sees through. What does "seeing through" mean? After spending a long time with a person, one comes to understand that person clearly, and will then make choices and decisions about whether to continue the association. Observing oneself works the same way. By constantly engaging in contemplative practice on the five aggregates of body and mind (pañcaskandha), over time one will see through the five aggregates—the principle is the same. Those with somewhat better wisdom may see through them a bit earlier; those with very poor wisdom will have to wait until a future life to see through them. But this foundation must be laid down, and the effort must be made.