Duty

"Suppose one of you had a servant plowing or looking after the sheep. Would he say to the servant when he comes in from the field, 'Come along now and sit down to eat'? Would he not rather say, 'Prepare my supper, get yourself ready and wait on me while I eat and drink; after that you may eat and drink'? Would he thank the servant because he did what he was told to do? So you also, when you have done everything you were told to do, should say, 'We are unworthy servants; we have only done our duty.' "
Jesus, in the Gospel of Luke

The chief end of man is to glorify God and enjoy Him forever. We exist to bring Him honor. He has made it clear how to do this: love God, love each other. If we live this way, our life is perfectly glorifying to Him and also perfectly satisfying to us.

But we don't. We sin. We seek to glorify ourselves instead of God, and we love ourselves above our fellow man. We can live a redeemed life and get closer and closer to holiness by the grace of Christ, but our nature is still sin. Our nature is sin, and our duty is holiness-- polar opposites. There is grace, oh praise the Lord, there is grace flowing down abundantly from the cross of Christ, and that grace will cover over all our sins, but let us not ever believe in our own achievements. Let us not ever say to God, "Give me the credit I deserve," for if He gave us all we deserved, we would be sadly surprised to find ourselves in Hell. Let us humble ourselves before Him, love Him and each other as He as asked, and ask nothing more than that our life would be a pleasant aroma to Him.

And in all of this, oh mercy of mercies, we truly find joy and peace.