What is the prerequisite for self-inquiry and discovery of the Atma?

The benefit we can derive from anything is proportional to the faith we place in it. From adoration of gods, pilgrimages to holy places, uttering mantras, or resorting to doctors, we derive benefits only according to the measure of our faith. When someone gives a discourse, the more faith we have in them as a scholar and an exponent, the more clearly and directly we can draw the subject into our hearts and understand the discourse deeper and deeper. For the growth of faith and for the fostering of understanding, an essential requirement is the purity of the heart, or purity of the kshetra (field), or purity of chittha (consciousness). Without this purity, the sudden effort of self-inquiry or investigation into the self-existent Atma, while in the midst of diverse worldly and material entanglements, will be rendered fruitless, since it will not stem from an eager will. The chittha must first be withdrawn from the objective world and turned inward toward the awareness of the Atma.

– Vidya Vahini, Ch 9.