Mullah Faizullah is the conscience perched on Mariam's shoulder. Even when things are the darkest, she can think about the scripture that he taught her and find some relief.
The Mullah is Mariam's only positive role model as a child. Mariam's relationship with Nana is close, but often tense. Mariam loves Jalil a great deal, but he just ends up disappointing her. Mullah Faizullah, on the other hand, always treats her with respect. He even encourages her to get a real education, much to Nana's dismay.
Most importantly, he teaches her a compassionate and practical brand of religion. Unlike the Taliban, who use the guise of religion to take power, Mullah Faizullah is willing to admit when he does not always "understand the meaning of the Koran's words" (1.3.20). His faith shaped Mariam and gave her the tools she needed to survive the many struggles that lay ahead.