Partially incomprehendable mystery. I don't ususally quote a lot of scripture in my posts because I'm trying not to be preachy. However, this seems to warrant it.
Psalm 8:3-5 - "When I consider Your heavens, the work of your fingers, The moon and the stars, which You have ordained. What is man that You are mindful of him, And the son of man that You visit him? For you have made him a little lower than the angels, and you have crowned him with glory and honour."
Though it is partially incomprehensible, the statement that we are "made in his image" is sort of an answer. We are the only creation of which that is stated. Man was made in the image of God to reflect Him. I don't know if that helps at all, but I gave it a whirl. You'll have to ask the Muslims, etc. why there God does, I'm not sure if the answer would be the same or not.