The ‘Self-inquiry’ is finding out the ‘Self’ which is hidden within the world, in which we exist. By inquiring ‘Who am I?’, the ignorance will not vanish. Without getting rid of the ignorance, the Advaitic wisdom will not dawn. Without the Advaitic wisdom, it is not possible to realize the truth, which is hidden within the world in which we exist.
That is why Sage Sri Sankara Says: ~ 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.
What is the use of saying ‘I AM THAT’ without knowing what the ‘Self’ is in actuality. Without knowing the truth of the Self, without realizing the truth of the world in which you exist it is impossible to realize the truth beyond the form, time, and space. By a mere utterance of the word ‘I AM THAT', the truth will not be revealed.