There are two aspects in the spiritual process. One is the awareness of truth (tatva jnana) and the other is religious meditation (upasana), say the Upanishads. They reiterate the need to realise the eternal truth of the Self and Brahman and also show us the paths that lead to this goal.
Any learning happens through the steps of hearing (sravana), contemplating (manana) and meditating (nidhidyasa) and hence their importance is emphasised especially when learning the import of the sastras, pointed out Sri K. S. Maheswaran in a lecture.
Sastras do not demand blind acceptance of what they teach. They encourage the mode of inquiry (vichara) which makes teaching/learning meaningful by allowing room for analysis, doubts, assumptions, etc. Each one needs to be convinced in his faith and belief in the inner truth. One is free to ask questions and also try to search for the answers. But to what extent one can ask questions and also get answers especially in matters of an esoteric nature? Moreover, not all answers are available in texts. There is no doubt that the buddhi or intellect is a useful tool to understand the profound thoughts in the Upanishads. Some with sharp intellectual attainments can be eloquent in theoretical aspects. But such proficiency need not necessarily be the result of realisation or enlightenment. Intellect can also help exercise its powers of discrimination in spiritual progress to perceive the distinctness of the Self from the body through an inward search. The intellect is also an instrument of the body and is a part of avidya (ignorance). The peculiar situation in which we are placed is that our senses, mind and intellect are drawn by the external world.
That is why the Katopanishad states: Many are not fortunate to hear of the Self. Others who have heard it may still not understand it. He who speaks of it is indeed gifted. More fortunate is he who is intelligent to learn about it. The most blessed is he who is able to understand it when taught by a good teacher who knows the Brahman as One.