The following is from a text written by Shankara called Vivekachudamani, as translated by Sri Ramana Maharshi. We will see the following points being made:

1. Merely stating ‘I am Brahman’ does not in itself lead to liberation. Similarly we can infer that by mere affirmation of other similar spiritual slogans such as saying ‘I am free’ or ‘I am already the Self’ or ‘there is no ego/self’ or ‘all is already one’, etc, mere affirmation of these does not lead to liberation.
2. In order to attain liberation, ignorance must be removed and the Self must directly be experienced.
3. Similarly, merely by hearing the truth ‘I am Brahman’ , liberation is not (usually) attained
4. One must first hear the truth from someone who has experienced the truth first-hand (for only they will be able to tell you the way to truth)
5. Then one must meditate upon the truth heard and experience the truth directly though constant meditation.
6. Unless this practice is carried out, maya (aka ignorance) will not be removed and liberation will not be attained.
7. Every effort must be made to root out ignorance for liberation to result

‘Just as a person’s sickness is not removed without taking medicine, so too his state of bondage is not removed by scriptural texts such as “I am Brahman” without his own direct experience of the Self. One does not become a king by merely saying, “I am a king”, without destroying one’s enemies and obtaining the reality of power.

‘Similarly, one does not obtain liberation as Brahman Itself by merely repeating the scriptural text “I am Brahman”, without destroying the duality caused by ignorance and directly experiencing the Self.

‘A treasure trove hidden under the ground is not obtained by merely hearing about it, but only by being told by a friend who knows it, and then digging and removing the slab that hides it and taking it out from below the ground.

‘Similarly, one must hear about one’s true state from a Guru who knows Brahman, and then meditate upon It and experience It directly through constant meditation.

‘Without this, the true form of one’s own Self, that is hidden by maya [“that which is not”], cannot be realised through mere argumentation. Therefore, those who are wise themselves make every effort to remove the bondage of individual existence and obtain liberation, just as they would to get rid of some disease.’

Also see: Sri Ramana Maharshi: the necessity of Meditation