Knowledge & its effect on purifying souls

From the book:

When one handles this significantly elaborate topic of soul purification and its aspects in light of verses and authentic aḥādīth, one deduces solid principles and comprehensive foundational rules that pave the way to purifying souls.

The most significant principle in this respect is that soul purification is a divine blessing. Allāh only sanctifies whom He wills. Allāh, the Almighty, says,

Have you not seen those who claim sanctity for themselves? Nay, but Allāh sanctifies whom He pleases. ” [Sūrah An-Nisā ’4:49]