Musar literature is didactic Jewish ethical literature which describes virtues and vices and the path towards perfection in a methodical way.
Musar literature is often described as "ethical literature." Professors Isaiah Tishby and Joseph Dan have described it more precisely as "prose literature that presents to a wide public views, ideas, and ways of life in order to shape the everyday behavior, thought, and beliefs of this public." Musar literature traditionally depicts the nature of moral and spiritual perfection in a methodical way. It is "divided according to the component parts of the ideal righteous way of life; the material is treated methodically – analyzing, explaining, and demonstrating how to achieve each moral virtue (usually treated in a separate chapter or section) in the author's ethical system."
Musar literature can be distinguished from other forms of Jewish ethical literature such as aggadic narrative and halakhic literature.
In Judaism, ethical monotheism originated, and along with it came the highly didactic ethics in the Torah and Tanach.
An example from the Tanakh is the earliest known text of the positive form of the famous "Golden Rule":
You shall not take vengeance or bear a grudge against your kinsfolk. Love your neighbor as yourself: I am the LORD.
Hillel the Elder (c. 110 BCE – 10 CE), used this verse as a most important message of the Torah for his teachings. Once, he was challenged by a ger toshav who asked to be converted under the condition that the Torah be explained to him while he stood on one foot. Hillel accepted him as a candidate for conversion to Judaism but, drawing on Leviticus 19:18, briefed the man: