The root first occurs in TaNaK in chapter 1 of the Book of Genesis, in verbal form, This phrase is interpreted by the sages of blessed memory, to mean "bear children, and raise them (or to make them great)". This mitzvah (commandment) of "raising" is given to fathers, but can be partially fulfilled through agency by appointing a mentor. "Rov" is a verb meaning "to raise" or to "make great", and the "Rav" is one who consciously takes on the role of "raising" sons, by teaching them the Torah, the law. Thus the Rav, the rabbi, is like a second father. A Jewish father is also obliged also to teach his son a practical trade whereby he may support himself and a family, and to teach him to swim.