The True Wisdom of Man
I just finished Calvin's Institutes of the Christian Religion, from 1536. The book was great but very difficult to read. I found myself re-reading to understand his arguments. This 920-page book can inspire and challenge the reader. I chose the Henry Beveridge translation from 1560 takes the Latin version and puts it into English. This is definitely a book to go slow with and re-read for comprehension. One pastor friend suggested reading the translation from French. If you are looking to stretch your mind, consider The Institutes.