What is emptiness? Everything is emptiness. The “substance” of anything isn’t actually there, but put together by thinking. When we look at a tree, there isn’t actually a “tree”, but thought says there is a tree, and associated with it the many scientific or emotional significance: like this tree was planted by me and I am attached to it, or this tree is classified according to the shape of its leaves, and so on. These are merely responses to the tree which are not the tree. Then comes the question: what is the tree? We can also ask: without thinking about the tree, is there a tree? There is no tree.
Identification with anything is a limitation. There is security in thinking that one is the body, the mind, a job, an identity, and so on. Yet implied in this security is the nagging insecurity, because anything within perception is transient, and the ultimate erasure of a separate existence is always pending. The job will end. The body will die. The mind will stop to exist. This is the root of the fear of death.
Identification limits consciousness to a particular part of itself. Consciousness then mistakes it to be only a part, but not the whole field. The field actually never changes, only the content of the field is transient. In such identification, the mind is never free, but bound by the illusory need to survive. In actuality, nothing survives, and such is the very freedom the mind is afraid of. Freedom is this very transience, is this constant change that goes on with abandonment and never looks back.