I have long argued, based on my own experiences, that the study of other religions is one of the best ways to lose your faith in the religion you were raised with. Brian Jay Stanley makes a similar point in this essay, part of a larger piece, in Sun Magazine.
Before college I was a skeptic and rationalist toward every religion except my own, Christianity. Like most of humanity, I had believed the religion I’d heard first, and on its authority dismissed all the religions I’d heard second. Seeing Muslims wearing turbans or Hindus bindis, I thought the oddity of their customs proved the error of their beliefs. Studying all faiths in one class in college, however, I saw my religion from the outside and realized that the rites of my Sundays — warbling choirs and smocked babies dipped in silver fonts and bread as the body of Christ — were as curious as what I had disparaged as myths. In class discussions I sometimes unwittingly revealed assumptions that I thought were axioms, and would read surprise in the eyes of a Hare Krishna or Bahai. My notion of normal was an accident of my birth and upbringing. Whomever I saw as strange saw me as strange. I had raised a doubtful brow at Buddhists bowing to golden statues, even as I prayed weekly to a crucified first-century Jew, not realizing that either all religions are bizarre or none is.
One of the big things that shocked me into reevaluating my belief in Christianity was learning about the Moabite stone (also called the Mesha Steele), a text from the Moabites that told their side of the story of the wars between them and the Israelites (the same wars discussed in the Bible in the third chapter of 2 Kings. At the same time that the Israelites were explaining their success or failure in war as the result of their Yahweh’s pleasure or anger with them, the Moabites were doing the same thing with their god, Chemosh. Suddenly I recognized that these claims were identical, so why believe the Israelite version and not the Moabite version? It was an important question in moving me toward skepticism.