I just finished reading The Letters of John and Abigail Adams. There are several excellent quotations and passages, and I especially liked this one from John to Abigail, 29 October 1775:
Education makes a greater difference between man and man, than anture has made between man and brute. The virtues and powers to which men may be trained, by early education and constant discipline, are truly sublime and astonishing. Newton and Locke are examples of the deep sagacity which may be acquired by long habits of thinking and study.