At the end of his book ‘The Salient Features of Sankara’s Vedanta’ (see link to download PDF below), Swami Satchitanandendra Saraswati (SSS) lists the key features of Shankara’s Advaita Vedanta.
Among them is the notion that liberation can result from either hearing the teachings (Sravana), reflecting upon the teachings (Manana) or meditating upon the teachings (Nididhyasana), depending on the maturity and fitness of the aspirant (we can see Sri Ramana Maharshi give the same teachings here). Not realising this, SSS notes that various commentators either say that sravana alone is the only way or that nididhyasana alone is the only way.
SSS then goes on to state that the way that these methods lead to liberation is by turning the mind inwards towards the Subject-Self (Atman).
Let us see what SSS writes on page 82:
6. Sravana (study of sacred revelation), Manana (reflective thinking) and Nididhyasana (concentrated contemplation), are all means for realizing Atman. Highly developed souls, however, who can immediately grasp the true meaning of the Vedic teaching, do not stand in need of any additional effort.
Not taking this principle into account is responsible for the divergence of opinion among commentators of Sankara Bhashya about the relation of Sravana and Nididhyasana. Of these, some assert that Sravana is the principal means and the other two are only ancillary to it; while others insist that nididhyasana is the one means to direct realization and without it mere Sravana would be of no avail.
7. Sravana and the other means are enjoined only so far as they turn the seeker inwards and direct him to stay his mind on Atman, but the resultant knowledge is no object of any injunction.
Tom: We can see that the purpose of Sravana, Manana and Nididhyasana are to turn the mind inwards, towards the Subject-Self (Atman), and that the resultant ‘Knowledge’ is not a result of any action or practice, but a synonym for the One Eternal Infinite Blissful Self that is ever-attained, ie. Liberation.
Please see here for Sri Ramana’s teachings on this same topic.
What is Vedantic Meditation? How Swami Satchitanandendra Saraswati (SSS) defines Nididhyasana
Shankara teaches two methods to ‘attain liberation’ | Swami Satchidanandendra Saraswati (SSS)
Ramana Maharshi: how to abide as the Self
Sravana alone can result in Self-Realisation! Sri Ramana Maharshi on Sravana, Manana and Nididhyasana