Not only is disinterested morality (doing good “for its own sake”) impossible; it is undesirable. That is, it is unbiblical because it would mean that the better a man became the harder it would be for him to act morally. The closer he came to true goodness the more naturally and happily he would do what is good. A good man in Scripture is not the man who dislikes doing good but toughs it out for the sake of duty. A good man loves kindness (Mic. 6:8) and delights in the law of the Lord (Ps. 1:2) and the will of the Lord (Ps. 40:8). But how shall such a man do an act of kindness disinterestedly? The better the man, the more joy in obedience.
John Piper