One of the six accessories to Vedic knowledge is called *niruktaM*. It was done by Yaska. It delves into the word-meanings of words found in the Vedas.
When dwelling upon the meaning of the word ‘shraddhA’ he says it originated from the two root words ‘shrat’ (indicative of Truth) and ‘dhA’ (which means ‘fixing’). So the integrated meaning of the word ‘shraddhA’ is to ‘fix something in the mind as the truth’ – in other words, to believe in something with conviction.
In Chandogya Upanishad (VII-19-1) there is a mantra which means: “This is the kind of shraddhA that we should have in that fundamental invisible subject, that should always occupy our mind; only then can we think right” -- *When there is shraddhA then and there is right thinking*.
Brahma-vidyA (Knowledge pertaining to the subject of brahman) should be taught only to those who have shraddhA – says Mundaka Upanishad. Who are those so qualified? The Upanishad gives a list of such qualifications. (III -2-10). Those who discharge their obligations (karmas) in the right manner; *shrotriyas* (those who have excellent scholarship of the vedas); those who have an intense anguish to be in brahman; and those who have shraddhA.
In Prashnopanishad also (I – 10) it says those who seek the Atman become eligible to do so by their tapas (austerities), celibacy (brahmacharya), shraddhA, and learning.
In the Gita, Bhagawan explains in one whole chapter the details of divine qualities as against the ‘asura’ (undivine) qualities and when he finishes this chapter, says: “He who transgresses the rules and regulations of the Shastras will get neither success nor happiness; therefore, O Arjuna, keep the Shastras as your pramANa (basic law) and decide on what to do and what not to do”.
Having said this, right in the beginning of the next chapter he says there could be an inborn shraddha, totally unrelated to Shastraic issues, and this could be in three different kinds, namely, rajas and tamas which are not desirable, but also a desirable sAtvic shraddhA. All this only shows the importance that one has to attach to the concept of shraddhA.