Why does God want us to worship him?
God doesn't need anything from us. He doesn't even need us to stroke his ego. Why, then, does he require us to worship him?
J. Budziszewski addressed this topic very briefly in his book, What We Can't Not Know and it got me to thinking about it.
We all recognize that we owe gratitude to people we recieve a benefit from. That's why we should thank somebody for a gift or a favour. Well ultimately, all gifts and things, and even our very existence, comes from God, so we owe the ultimate gratitude to God. That's basically what Budziszewski said, but don't take that as a quote, because it's just the general idea I got from him, and that was several months ago.
Since morality has its origin in God, then God must enforce what's right--even the ultimate gratitude that we owe him. Worship is the expression of that ultimate form of gratitude.
It has nothing to do with God's ego. In fact, it's not even possible for God to have an inflated ego. Anselm defined God as a being than which none greater can be conceived. Not even God can conceive of a greater greatness than his own, because no greater greatness is possible.