"Joy In the Doing"
"I take joy in doing your will, my God, for your law is written on my heart."
To know the will of God and to take joy in doing it are two different things! Many of us do not really want to know what God wants us to do because we might not want to do it once we know it! If we are inwardly honest and sincere, we will determine to find God's will and then set about joyfully obeying.
While Jesus was on earth, he explained his mission: "For I have come down from heaven to do the will of God who sent me" (John 6:38). The Son of God was not talking about a trip around the world--a luxury cruise through the universe. He was talking about the will of God for him, which involved suffering. Yet he delighted to do it because God wanted it!
It isn't easy to do the will of God when his will for us is difficult or involves suffering. It isn't easy to say no to a relationship or a job, even when we know that it is not God's will for us. It isn't easy to say yes to a difficult step or a move across the world, even when we know it is God's will. Notice that the psalmist took joy in "doing" God's will, not just in "knowing" it. Yet can we obey God, knowing the joy "set before us" at the end of the day? It may not be easy at first, but God promises that we will have great joy in the doing.
For further study: Psalm 40:6-10