What is in Emptiness?

Emptiness is advocated by both Buddhism and Taoism alike which is why they are often misinterpreted as negative nihilism. The problem lies in jumping into conclusion after looking at the surface or a fragment of the whole.
This can be best illustrated with the sky above our head. Its vast, empty, full of space; yet it is versatile, volatile and dynamic, full of potentials. It reveals the Sun and the Moon; it carries everchangable- clouds; it nurtures rains, wind, storms, thunder; and most important of all it is a vehicle for the very air we breathe in. In a word, the sky is by no means sterile and inert. Because of its emptiness and seemingly passivity (non-imposing), docility (non-interfering) and receptivity (non-invasive), all activities that are necessary for nurturing life on earth are allowed to take their own course on our planet.
This is exactly the state of being an illumined person has reached. His mind is devoid of all conditioning, all perceptions, all contrivances, all artfulness, all judgements and discrimination. He is free because his mind is not compelled to go in any direction or pulled this way or that by old habits, inertia or external influences. The emptiness of his mind has meshed with the emptiness of the Universe simply because of the affinity between the two. In other words, the union is not a result of contrived effort from the individual (through faith, doctrine or belief systems); neither is it the work of Divine Grace. God doesn't show favourtism; He doesn't pick you up just because you worship or pray to him. If the sky is blocked by dark clouds and you cannot see the sun, what would be the use to pray to or worship the Sun to show itself to you? If our mind has been made opaque by all manners of defilement, how can our soul be illumined by light from Heaven?
True meditation can only happy when the mind has been rendered quiet, passive and empty. Then it will be filled with the Otherness. This is exactly what Jesus was trying to teach when he said, "Empty yourself and I will fill you up." Any effort from the mind to grasp at things, project things will only make it unfit for meditation.
The human body is a reflection of the universe in microscopic scale. When one sits in quiet meditation (genuine meditation, not sitting posture coupled with mental gymnastics) devoid of tension, the body will start trembling of its own accord. This is because energy(chi) and vitality (chin) within, which has been locked up by accumulated tension of the body and mind, has once more been allowed to take their own natural course. Once the space is created, real genuine movements and dynamics will take place.
Such a state is described in detail by Lao Tze in Tao Te Ching:-

      Such the scope of the All-pervading Power

That it alone can act through the Way.

For the Way is a thing impalpable,

incommensurable.

Incommensurable, impalpable.

Yet latent in it are forms;

Impalpable, incommensurable

Yet within it are entities.

Shadowy it is and dim;

Yet within it there is a force,

A force that though rarefied

Is none the less efficacious.  

[Chapter 21 Tao Te Ching as translated by Arthur Waley]