This book is always free -- I'm mentioning it now because it is arranged by calendar for a year's study. George MacDonald was a great influence on C.S. Lewis, and this book is a good introduction to his works...
A Book of Strife in the Form of The Diary of an Old Soul by George MacDonald
On Gutenberg:
http://www.gutenberg.org/ebooks/1953
Read reviews on Goodreads:
https://www.goodreads.com/book/show/..._Old_Soul?ac=1