This universe is common to all of us, therefore one must include the universe his investigation in order to realize the ultimate truth or Brahman.

This universe is common to all of us, therefore one must include the universe his investigation in order to realize the ultimate truth or Brahman. It is only after one has inquired into the nature of the objective universe, that he should inquire into who is the knower. If, however one inquiries into the knower before the inquiry into the universe, then it is mere mysticism. One must have the perfect understanding of what is what.

“What is this  universe?

What is this ‘I’?

That is why Sri, Sankara indicated in (VC):- 63. Without causing the objective universe to vanish and without knowing the truth of the Self, how is one to achieve Liberation by the mere utterance of the word Brahman? — It would result merely in an effort of speech.

65. As a treasure hidden underground requires (for its extraction) competent instruction, excavation, the removal of stones and other such things lying above it and (finally) grasping, but never comes out by being (merely) called out by name, so the transparent Truth of the self, which is hidden by Maya and its effects, is to be attained through the instructions of a knower of Brahman, followed by reflection, meditation and so forth, but not through perverted arguments.
--FORMLESS PATH