Those who know him who is to be grasped by the mind, who is not to be called the nest (the body), who makes existence and non-existence, the happy one (Siva), who also creates the elements, they have left the body.

In plain words: God can be grasped by the mind, but he is not the body, which is just a 'nest'. He is Shiva, the happy one, who makes what exists and what does not, and creates the elements. Those who know him have left the body behind.