No crops can grow on barren land. Requiring favourable soil for their growth, they must grow on fertile land. So also does tazkiya require favourable soil from which to grow. And that favourable soil is modesty. The quality of modesty greatly facilitates the attainment of tazkiya. On the contrary, arrogance is unfavourable to its attainment. An arrogant person can never attain the goal of self-purification. The most significant feature of modesty is that it causes a person to feel that there is something lacking in him.
The result of this feeling is that when the truth becomes evident to him, he accepts it without any reservation. He receives it in an unbiased way and soon discovers that this truth can compensate for his shortcomings. Thus, he accepts the truth as if it belonged to him. This quality is the spirit, or essence, of tazkiya. The case of an arrogant person is quite the opposite. The thinking of an arrogant person is that he already has everything and need not take anything from anyone. For this reason, he is not able to accept advice from others. He rejects the message of the reformer. This attitude becomes an obstacle to his taking to the path of tazkiya.
The truth is that tazkiya, a continuous process, can have its effect only on a modest person. Modesty enables one to accept the truth and frees one from psychological complexes. Only a complex-free soul (The Quran, 89:27) can succeed in attaining the goal of tazkiya.