Growth. Growth comes from religion. People who believe are inspired by that belief. That inspiration encourages them to act on a grander scale. Those actions and the consequences of those actions form the basis for their growth.
People that don’t believe are stuck operating in frames limited to human understanding. Human understanding is limited by ignorance, God is not so limited. When you allow God to choose your path and the outcome from following that path, what follows is bound to make you grow.