Albert Barnes on Luke 17:10

Are unprofitable servants. We have conferred no favour. We have merited nothing. We have not benefited God, or laid him under obligation. If he rewards us, it will be matter of unmerited favour. This is true in relation to Christians in the following respects:

1st. Our services are not profitable to God (Job 22:2); he needs not our aid, and his essential happiness will not be increased by our efforts.

2nd. The grace to do his will comes from him only, and all the praise of that will be due to him.

3rd. All that we do is what is our duty; we cannot lay claim to having rendered any service that will bind him to show us favour; and

4th. Our best services are mingled with imperfections. We come short of his glory (Rom 3:23); we do not serve him as sincerely, and cheerfully, and faithfully as we ought; we are far, very far from the example set us by the Saviour; and if we are saved and rewarded, it will be because God will be merciful to our unrighteousness, and will remember our iniquities no more, Heb 8:12.

(f) "unprofitable" Job 22:3, Ps 16:2,3, Is 64:6, Rom 11:35, 1Cor 9:16,17