We humans have religion because we don't know how we ought to live. We understand the how of many things, and most of us are confident that, in time, science will reveal that which we presently do not know. Yet we do not know how we ought to live. We know how we CAN live, but whether or not we should live in some of the ways we can live--in a manner best for us as individuals (self-serving or for survival), as a community of humans (for your country, religion, or humanity as a whole), as part of a web of life, or as a part of our planet--is simply beyond us.
Everyone has ideas; nobody has authority.
So, we as individuals do one of two things. We either admit that the question of "How we ought to live" is completely subjective and do our best to live well with that always in mind, or we seek an authority which will tell us how we ought to live and thus give us the comfort of believing that there is a purpose for our actions.
Because other mortals have the same problem we do, (not knowing how they ought to live), we need more than a mere human authority; we need an authority guided by divine inspiration. Without this, we are forced to admit that we aren't really sure if the way we are living is "right". If it is possible that we are not living correctly, then every action we do during our lives becomes questionable. For example, if the purpose of our lives is not to serve God, then we've been wasting a lot of time going to church. If we're not supposed to conquer the earth and bring it under our power, then we've been destroying nature needlessly.
For many of us, that is just not acceptable. We want our lives, and the things we do during our lives, to mean something. We don't want our actions to be wasted, unnecessary, or flat out wrong. We want to believe that our way of life is helping keep the world on track, helping the world fulfil whatever destiny it is "meant" to fulfil, for this means that there is a purpose to our lives; we exist because we have a purpose to fulful--to help the world (planet or humanity) as a whole achieve its destiny.