JC - Chapter 27

After the apostles had requested of the Savior -

"...Increase our faith."  (New Testament | Luke 17:5)

...the Lord taught this parable -

"...which of you, having a servant plowing or feeding cattle, will say unto him by and by, when he is come from the field, Go and sit down to meat?
8 And will not rather say unto him, Make ready wherewith I may sup, and gird thyself, and serve me, till I have eaten and drunken; and afterward thou shalt eat and drink?
9 Doth he thank that servant because he did the things that were commanded him? I trow not.
10 So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do."  (New Testament | Luke 17:7 - 10)

Elder Talmage comments -

"The servant might well feel that after a day’s work in the field he is entitled to rest; but on reaching the house he finds other demands made upon him. The master has a right to the servant’s time and attention; such was among the conditions under which the servant had been engaged; and while his employer might thank him or give some substantial reward, the servant cannot demand such recompense. So the apostles, who had given themselves entirely up to their Master’s service, were not to hesitate nor demur, whatever the effort or sacrifice required. The best they could do would be no more than their duty required; and, without regard to the Master’s estimate of their worth, they were to account themselves as unprofitable servants."

Obviously, our duty is whatever is asked of us.  Mosiah taught -

"...if ye should serve him who has created you from the beginning, and is preserving you from day to day, by lending you breath, that ye may live and move and do according to your own will, and even supporting you from one moment to another—I say, if ye should serve him with all your whole souls yet ye would be unprofitable servants."  (Book of Mormon | Mosiah 2:21)