I found the quote listed below very insightful from Martin Luther on the nature of motives. This comes from "A Sermon on the Three Kinds of Good Life."
He who seeks nothing other than holiness is the one who seeks God himself, and he will find him. He who seeks reward, however, and avoids pain, never finds him at all and makes reward his God. Whatever it is that makes a man do something, that motive is his god.