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."
The terrible paradox is that this struggle is hardest for those for whom religion is the most important. The more people believe the teachings of their religion, the more they are attached to their religious community, the more painful their inner conflict can be.
Fortunately, although slowly, this is changing. In hopeful and exciting ways, for those who has reached the top of the Mountain are achieving positive changes within traditional institution, as well as creating new faith communities in which the spiritual value of all people is affirmed and celebrated.
In his own hearts and minds, spirits and souls, he is searching for and finding his own authentic spiritual connection. He is coming to his own understanding of God and affirming a spirituality that celebrates the value, dignity, and precoousness of all people.
Baldwin's relationship with religion was complicated. This is his most biographical novel, and arguably his most religiously themed. Baldwin never professed association with a denomination or congregation. That being said, religion was constant theme in his writing from beginning to end, and it is not completely negative. When friends would visit him in Harlem in his latter life, he would invite them to go with him to local storefront (pentecostal) churches. For Baldwin, religious experience was an important place of meaning, though it had clearly run off the rails in the case of his father. Despite Baldwin's longterm issues with father figures (he also scorned Richard Wright, who helped him to find funding for his Paris sojourn), his opposition to his father was not to religion per se but the way his father lived it. Later in his life Baldwin downplayed his conversion experience, but in his early and mid life he still gave the event signficance. Baldwin would share a strong moral consciousness, that can be argued is the strongest continuity from his religious heritage.
In short, "Go Tell It on the Mountain" is not a negative take on religion. Instead it offers various visions of religion, some very negative and some positive (in a qualified way). Most of all, it recognizes religion as a potent force of meaning in black and human life.