From YOUCAT, fact 2:
2: Why did God crate us?
God crated us out of free and unselfish love.
When a man loves, his heart overflows. He would like to share his joy with others. He gets this from his Creator. Although God is a mystery, we can still think about him in a human way and say: Out of the “surplus” of his love he created us. He wanted to share his endless joy with us, who are creatures of his love.