Refer to verse 2 of Atma Bodha:
बोधोऽन्यसाधनेभ्यो हि साक्षान्मोक्षैकसाधनम ।
पाकस्य वह्निवज्ज्ञानम् विना मोक्षो न सिध्यति ॥२॥
bodhonyasādhanebhyo hi sākṣānmokṣaikasādhanama |
pākasya vahnivajjnānam vinā mokṣo na sidhyati ||2||
Which literally translates as: Just as the fire is the direct cause for cooking, so without Knowledge, there is no emancipation. Compared with all other forms of discipline, the Knowledge of the Self is the one direct means for liberation.
According to this verse of Atma Bodha, in the process of cooking, ingredients can be substituted, but fire is essential and has no alternative. Similarly, there are alternative paths that people may take for seeking the Self, but the Knowledge of the Self is essential for mokṣa – liberation.
Also, refer to the Bhagwad Geeta (4-37) in which Krishna says that as the blazing fire turns firewood to ashes, so the fire of knowledge burns to ashes all reaction to material activities. Jnāna burns all āgāmi karma and liberates a person. And further, Krishna says (4-41,42) that one who has renounced the fruits of his action, whose doubts are destroyed by transcendental knowledge and whose mind is firmly seated in the Self, is not bound by action. So the doubts that have arisen in the mind out of ignorance can only be slashed by the weapon of knowledge.
Reference text: Bhaja Govindam by Adi Shankara, commentary by Swami Chinmayananda