Tazkiyah literally means purification. In the extended sense it means growth. In this respect, Tazkiyah means intellectual development. The mind is not something stagnant, it is ever-growing, like a tree. It is this process which is called “adding faith to their faith” (48:4) in the Quran. Adding faith to faith means development in consciousness, which is another name for intellectual development. The real faith is one which does not stagnate, but grows continuously in its conviction about God.
How does Tazkiyah or intellectual development take place? The path to this is contemplation. "Contemplation" is in itself a continuous process – contemplating the Quran and Hadith, the life of the Prophet, the lives of the Companions, the various human disciplines, the universe, the earth and the heavens. There is also the kind of contemplation which takes place during serious discussions. In this process of contemplation, new ideas emerge, deeper meanings come to light, new aspects hitherto unexplored of different events and realities are discovered, and every experience will bring him closer to God.