"Will any of you who has a servant plowing or keeping sheep say to him when he has come in from the field, 'Come at once and recline at table?' Will he not rather say to him, 'Prepare supper for me, and dress properly, and serve me while I eat and drink, and afterward you will eat and drink? Does he thank the servant because he did what was commanded? So you also, when you have done all that you were commanded, say, 'We are unworthy servants; we have only done what was our duty."
The word for unworthy, 'achreioi' in the Greek comes from the word, 'chreioi' meaning useful. The prefix, 'a' added to it signifies the opposite of useful: useless or worthless. Some translate the word to mean 'unprofitable.'
Think of that for a moment: the God who owns all things and has need of nothing, calls us to himself and then sends us out into the world to serve Him. But as we serve Him even the best of our efforts are useless, worthless and unprofitable. Quite literally, by enlisting us to serve Him, God, operates His kingdom at a loss.
Think of it this way: He could've chosen a more efficient and profitable means of getting the job done. Yet, He has chosen to use people like you and me, to be His servants. Paul describes us as jars of clay -- cracked earthen vessels (II Corinthians 4) into which God has poured His treasures.
As you go forth into the world keep these thoughts in mind. Some are tempted to exaggerate their own importance in the Kingdom of God. Deep down they think that God is happy to have them on his team; that He is glad for their gifts and contributions to His kingdom. But the Scriptures prove otherwise. Though He has employed us as His servants He could've quite easily created a more efficient way of getting the job done. By utilizing fallen people like ourselves he operates His kingdom at a loss.
"For who has known the mind of the Lord, or who has been his counselor? Or who has given a gift to him that he might be repaid? For from him and through him and to him are all things. To him be glory forever! Amen." Romans 11:34-36.