“I take joy in doing your will, my God, for your instructions are written on my heart.”” (Psalm 40:8, NLT)

The Emphasized Bible has: To do they good pleasure, O my God, is my delight. 

To the Jews there was an intimate connection between being a God-worshipper and doing his will. They would have been flummoxed by a propensity to preach grace if we did not also emphasize following God’s commands. If we are not willing to obey God with a willing heart, then how could we possibly be devoted to him at all? And didn’t God give his commands so we would flourish? Weren’t God’s directions to us meant to help us navigate through the shoals of life without running aground and sinking? What kind of person wouldn’t see the value in that and pursue it and God with all their might.

We would do well to listen to David. It is not duty to do God’s will, it is delight!