Heidi has been, off and on, one of the top-rated ebooks on this site, beating out better-known classics of British and American literature. Written in 1880 by Swiss author Johanna Spyri, Heidi focuses on events in the life of a young orphan who is pawned off on her hermit grandfather at a young age. Heidi's innate goodness and loving attitude has a deep effect on those around her, including grumpy gramps, helping them to realize the error of their ways and changing their lives for the better.
Much more than a tribute to the goodness of human nature, Heidi is also a paean to nature and her produce (namely the produce of Swiss milk goats). Be forewarned: if you love dairy, you will want to eat cheese and drink milk every time you pick up this book. I recently read Weston A. Price's classic Nutrition and Physical Degeneration, and particularly the chapter on "Isolated and Modernized Swiss" reminded me of Heidi. From the amount of raw dairy Heidi ingests in this book, no doubt she and her kin have very strong teeth and bones!
You will also need a handkerchief, as Heidi's heartwarming antics will produce misty eyes every time. Not only is this book full of wholesome ideals, it is also very charming. Where Louisa May Alcott and similar authors of young adult literature may verge on sappiness, Spyri conversely wraps the most endearing story in truthful, honest prose.
There are several references to God's teachings in this book, which some reviewers think classifies Heidi as strictly religious material. However the references aren't overtly of any particular religion. And the basic religious principles Heidi learns are founded in common sense and courtesy. Heidi--as all the best literature, young adult or not--has something for readers of all ages and beliefs.