Pure faith means clear, undoubted confidence in believe. With only “believe”, it is still not considered as undoubted faith. In reality, if one does not truly understand the meaning of what one hears or sees, then it cannot be regarded as undoubted faith.
That is why, it is important that we should have proper understanding of the meanings, and so we say, “Now I realize, that Buddha has such limitless and boundless spiritual powers!” When you feel such reciprocations in your heart, a pure faith will then arise.
For instance, if someone should tell you to recite the sutras or names of Buddha and Bodhisattvas, and after these recitations you attain special merits, either through some reciprocation from the Buddha and Bodhisattvas, or if any terminal disease is being cured; lo and behold, you now know what this faith is about. Or if you should understand some logic of the dharma, knowing that it will help you to remove your troubles. You follow suit and these troubles are really removed. So at that moment, your understanding of the Dharma, is that it is able to purify the troubles or problems you have in your heart, and that is how you are able to align yourself with the Dharma.
This is what we call pure faith-- the Buddha’s inconceivable great spiritual merits. Hence in your heart, arises a proper right faith which becomes an unshaken force.
Extracted from: Venerable Master Jih Chang’s “The Great Treatise On The Stages Of The Path To Enlightenment”, Master’s Handwritten Discourses Volume 12