People, in this novel, are good and evil. Religion is neither good nor evil but serves varying purposes depending on the characters we choose to look at. Religion is clearly a central element of the novel and has a great power over the family and community life depicted in the book.
Isolating or reducing the value of religion, however, down to a qualification of good or bad will lead us away from identifying the way that John's religious experience forms the positive basis for his maturation and the way that John's father uses religion as a means to dominate his family (negatively).
Another character, Elisha, has a positive connection to religion and to John. If Elisha were the only figure in the church, we would certainly say that religion has a positive value in the novel.
The mixed values associated with religion and religious experience can be found in this line, uttered by Gabriel after John's ecstatic experience:
His stepfather is hesitant to believe in John's spiritual conversion and points out that "it ain't all in the singing and the shouting—the way of holiness is a hard way."