John Piper, The Dangerous Duty of Delight, 2001, p. 54.
The widespread notion that high moral acts must be free from self-interest is a great enemy of true worship. Worship is the highest moral act a human can perform; so the only basis and motivation for it that many people can conceive is the moral notion of disinterested performance of duty. But when worship is reduced to disinterested duty, it ceases to be worship. For worship is a feast of the glorious perfections of God in Christ.
John Piper, The Dangerous Duty of Delight, 2001, p. 54.