Why Does God Command Us To Worship Him?

Though I disagree with much of John Piper's soteriology (and advise discernment when listening to his and all other sermons and teaching), I take joy in agreeing wholeheartedly with his focus on the act of worshiping God. God is the only person for whom a demand to be worshiped is not classified as megalomania, since it is for the completion of our joy that God demands worship.