External and Internal Conflict

I finished this book, and after basking in the afterglow of Hurston's masterpiece, I wondered, "why is it called Their Eyes Were Watching God?"
God was mentioned, certainly, but on pure volume of content alone, religion was not the major theme in this novel. By such a standard, God has no place in the title of this book.
I would argue that the major theme of this novel is a teaching on the importance of being yourself, of individuality. Through this lens, I began to understand why God was such a large part of this novel, whether mentioned often or not.
(warning: I'm not bashing religion. Really. If you are a believer I think that is a wonderful thing; I am NOT passing judgement. These are simply generalizations about history)
Looking at the history of religion (I'm sticking to what I know- Judo-Christian religions), you can see that as we, as a society, progressed towards self-sufficiency, we became less and less religious. In the early days, when there was no such thing as science to explain death, birth, and nature, people created the idea of a God to help them to understand and explain things. Unsure of themselves and where they came from, they relied on God. Even as recent as colonial America, Calvinism and other forms of Christianity that favored an all-powerful and merciless God were popular. This was, again, during a time when people had difficult lives, unaided by modern science. They subscribed wholly to an omni-present God because they could have confidence in such a God, when they could not have confidence in themselves and their ever-changing society.
In Hurston's time there was the advent of modern electricity and other conveniences, that made it possible for people to live without difficulty, and with assurance in how the world works and, to a point, how their day to day life would be. It was this self-assurance that allowed them to be independent individuals. It also made their reliance on God less urgent; they needed God less, and so they questioned him more.
Also, black people in America were going through a dramatic coming of age. When enslaved, black people had no choice but to turn to God for hope and consistency in a life they themselves did not own. Individuality was impossible; Independence unthinkable. Upon emancipation, former slaves were thrust into a state where they could finally rely on themselves rather than God, and so they began to watch him with a careful eye.
In Their Eyes Were Watching God, a pivotal internal conflict of every character, and the psyche of black American society as a whole, is that of whether to believe in God, or believe in themselves.
The quest for individuality that is so central in this novel, is irrevocably intertwined with Hurston's constant questioning of God. Therefore, the presence of God in this novel, in the title, and more specifically, the ongoing conflict over faith, serves to further develop and enhance the main theme, which is the importance of individuality.