"Nefesh HaChaim" is a foundational work of Jewish philosophy written by Rabbi Chaim of Volozhin in the 19th century. The text emphasizes the importance of the soul and its connection to God, exploring how spiritual practices and Torah study can elevate one's soul. It serves as a guide for understanding the inner workings of the soul and its relationship with the divine. The book is divided into four sections, each addressing different aspects of spirituality, prayer, and the significance of mitzvot (commandments). "Nefesh HaChaim" has had a lasting impact on Jewish thought and is often studied in yeshivas to deepen one's understanding of the soul's role in religious life.