The aim of Upanishadic teachers were to establish a way of knowledge to enable those who meditated in a certain way at length adopted a particular technique attained complete identity with Primal Being which underlies all existence.
The idea of complete identity is summed up in Chandogya Upanishad
“TAT TVAM ASI”
Meaning that individual soul has realized its identity with Brahman who is unqualified absolute.
When the above is realized then release from all the hampering conditions of life of Phenomenal World of Time and space, which is illusory, becomes possible. This is Nirvana the passionate peace.