David Brainerd a Missionary to the Indians - Get his Diary Book, it's very encouraging

Oh, That I May Never Loiter On My Heavenly Journey!
Reflections on the Life and Ministry of David Brainerd
1990 Bethlehem Conference for Pastors

http://www.desiringgod.org/ResourceLibrary/Biographies/1461_Oh_That_I_May_Never_Loiter_On_My_Heavenly_Journey/

You can buy the book here:

http://www.amazon.com/Life-Diary-David-Brainerd/dp/1598560530