Rabbi Yitzchak Breitowitz: Sefer Nefesh Hachayim

In his Sefer Nefesh Hachayim, Rav Chaim of Volozhin (foremost pupil of the Vilna Gaon) sets out many fundamental Jewish beliefs, such as the profound impact that our mitzvos and prayers have on the universe; an understanding of brachos (blessings), the nature of the soul and of Olam Haba (the World to Come); whether one should combine Torah study with earning a livelihood, and whether man is greater than the angels, to name just a few.

Rabbi Gideon Weitzman: Taking Medicine on Pesach