The following quotes are from a book by C. H. Spurgeon called An All-Round Ministry: Addresses to Ministers and Students (p.70-72).  I have pulled some paragraphs out that I thought especially encouraging to those who minister in small or discouraging fields.

“Remember, dear brother, if you give your whole soul to the charge committed to you, it does not matter much about its appearing to be a somewhat small and insignificant affair, for as much skill may be displayed in the manufacture of a very tiny watch as in the construction of the town clock; in fact, a minute article may become the object of greater wonder than another of larger dimensions.  Quality is a far more precious thing than quantity.”

“We must never think, because the particular work we have in hand seems to be insignificant, that therefore we cannot do it, or should not do it, thoroughly well.  We need Divine help to preach aright to a congregation of one.  If a thing is worth doing at all, it is worth doing well.  If you had to sweep a crossing, it were well to sweep it better than anybody else.  If you only preach in Little Peddlington, let Little Peddlington know that you are doing your best, and seeking its good.  Many a minister has achieved fame, and, what is far better, has brought glory to God, in a congregation which could be counted by units, while another has presided over a large church, and though at first there was a great blast of trumpets, it has ended in the silence and sadness of utter failure.  Know your work, and bend over it, throwing your heart and soul into it; for, be it great or small, you will have to praise God to all eternity is you are found faithful in it.”

“Come fair or come foul, my comrades, hold ye the fort.  Some men attempt to excuse their own negligence by blaming the times.  What have you and I to do with the times, except to serve our God in them?  The times are always evil to those who are of morbid temperament.”

“Charles the Twelfth of Sweden had his secretary sitting by his side writing from dictation, when a bombshell fell through the roof into the next room.  The secretary, in alarm, dropped his pen, upon which the king exclaimed, ‘What are you doing?’  The poor man faltered, ’Ah, sire, the bomb!’  The king’s answer was, ‘What has the bomb to do with what I am telling you?’  You will say that the secretary’s life was in danger.  Yes, but you are safe in any case, for you are side by side with Jesus in holy service, and no evil can befall you.  Watch on, and work on, even to the crack of doom.  Leave the times and the seasons with God, and go on with your work.”

“Carlyle speaks somewhere of the house-cricket chirping on while the trump of the archangel is sounding; --who blames it for so doing?  If God had made you a house-cricket, and bidden you chirp, you could not do better than fulfill His will.  As He has made you a preacher, you must abide in your vocation.  Even if the earth should be removed, and the mountains should be cast into the midst of the sea, would that alter our duty?  I trow not.  Christ has sent us to preach the gospel; and if our life-work is not yet finished, (and it is not), let us continue delivering our message under all circumstances till death shall silence us.”