All too often, in discussions about the 'will of God', the greatest source for information about God's will, the Bible, is forgotten.  So sad.  In this passage, Jesus does us all a favour by cutting through the mass of biblical material on what God wills for his children by boiling it down to its irreducible minimum.  As if to say, if you know this, you know the main thing about the will of God.  Wouldn't that be helpful?