"The clearer the diamond, the more it sparkles; the plainer the heart is, the more it sparkles in God's eyes. What a commendation did Christ give Nathaniel - 'Behold, an Israelite indeed, in whom is no guile.'" - Thomas Watson, as quoted in Spurgeon's Sermon Notes
Further recommended reading & listening:
The Best of The Daily Spurgeon
The Forgotten Spurgeon, by Iain Murray
A Defense of Calvinism - by Charles Spurgeon