I'm a Christian existentialist, so I think that one of the ways God expresses love for us is by making us "in God's image"--that is, by giving us self-determination. So we are given the grace to experience existence in a way similar to God.

Of course, you said that "we don't have any [religion]," so I'm going to say that my explanation isn't going to do it for you. In that case, I'd say that you have to construct your own meaning. That's part of what makes life enjoyable.

For what it is worth, as I begin to figure out what I want to do with my life more and more, I am less and less concerned about what my life's meaning is. My planned vocation (lawyer/deacon) seems to be fitting that hole in my life very nicely. I had an interesting experience flying last week. I looked out the window and saw a small community down below, and I realized that truly serving that community as deacon would be more than enough work to last a lifetime. Now, that's not what I want to do with my life, but it was a very enlightening moment.