The Mandakaya Upanishad describes the Soul; The Atma thus – “That which cannot be seen and captured in the net of relativity, speech and the other sense organs cannot describe it. That which has no distinguishing features. That which cannot be grasped by the thoughts or ever described by speech, nor which arises from memory, that which unites everything; The Atma; has to be realized.
This verse from the ancient Indian scripture describes, both the Atma; as well as the Paarmatma; the Soul and God. This probably answers the question, why none has been able to describe God; even the Buddha or Adi Shankara.
What we learn from this is that there is absolutely no difference between the Soul and God; the Soul is the God Particle present in each and every living thing.
This substantiates the fact that realization or Nirvana can always be experienced in the “Singular”. There exists no plural; the plural is only a deception of the senses; Maya. This is why God can never be described.
The Buddha described his Nirvana to his disciples thus “I achieved the supreme state of ego annihilation not subject to decay, death, sorrow and defilement. The knowledge; as a thing arose in me; my liberation is total. I am free from the cycle of birth and death”
Even the Buddha could not describe Nirvana; in another discourse to his followers he said “There is an unborn, a non being, an unmade, an uncompromised. If It was not so then there would be no escape from that which is born, become, created and compounded.”