Lessing, Gotthold Ephraim "Nathan the Wise" (German: Nathan der Weise) - 1779
If you are looking for a non-English classic, this is one that has survived all changes of time and is as actual today as it was in the past. A masterpiece about philosophy, about Jews, Christians, Muslims, and that they are all equal, apparently it was revolutionary in 1779, well, I think it still is revolutionary today.
The way the three monotheistic religions are depicted and the problems between their followers shown is precise and still as true as ever, sadly.
A great, important part of literature. Read it, you will enjoy it.
From the back cover:
"One of the most frequently performed and widely read comedies of the eighteenth century, Gotthold Ephraim Lessing's 'Nathan the Wise' (1779) combines rich characterization with an engaging plot. Set in Muslim-ruled Jerusalem at the time of the Crusades, it deals with universal themes -- including the nature of God, antisemitism, wealth and poverty, and the conflict between love and duty. Today the play is as timely as ever."