Sentence:  A contrast of the scripture reading of , let us say , St. Augustine , John Bunyan , and Thomas Jefferson , all three of whom found in such study a real <WSD>source</WSD> of enlightenment , can tell us a great deal about these three men and the age that each represented and helped bring to conscious expression . 
Meaning of the word marked with <WSD> tags:  anything that provides inspiration for later work