Introspection is a major source of tazkiyah. Introspection awakens the human mind, it jolts the human personality, it gives the individual the incentive to reform himself. In this way introspection leads one to intellectual and spiritual development.

For instance, suppose someone said something which hurt you, you were provoked and you reacted negatively. Later, you became repentant and engaged in introspection, which led you to think that by having behaved in this way, you were developing a negative personality, such as would have a deleterious effect in the life after death. Such a negative personality would, indeed, render one incapable of gaining entry into Paradise.

Thinking born of introspection is the greatest source of tazkiyah. Tazkiyah can always be achieved by inner self-appraisal, rather than by some external activity.