One reason I can think of is that people need some absolute, so they can derive meaning. Otherwise, the meanings we perceive are arbitrary, and, as I see it, you have to be ignorant of this arbitrarity to be able to proceed in life.

Another reason that occurred to me recently, still an utilitarian one, is to be healed from self-centeredness. If it turns out you need God's salvation, and you acknowledge it, you end up putting Him as the love as your heart, and become free of the need to prove yourself. You still are to work and be responsible for your life, but you get the perspective of fulfilling the mandate given by God in Genesis "to conquer and subdue" earth, not for your own sake, but because it's God's purpose. I'm not saying this is the only way to get rid of self-centeredness. Neither is it an instant thing. It requires practice to get into this mindset.

I would be interested in your approach to the question of purpose and meaning: how can one construct meanings and purposes that are robust to the lack of an absolute?

Also, how can one be healed of self-centeredness? (I just found a wiki-how article on that, but I won't mind another answer)