From one’s bar mitzva onward, two angels accompany the person. When he walks a straight path they rejoice with him, but if he walks a crooked path they abandon him.

The Holy One, blessed be He, does good for mankind, as once one reaches the age of thirteen, He places with him two guardian angels to guard him, one to his right and one to his left. When one walks a straight path, they rejoice with him and encourage him to be happy; they proclaim before him: Give honor to the image of the King. But when he walks a crooked path they mourn for him and distance themselves from him. (Zohar 2:106b)

A person possesses a holy soul, and it begins to bond with him at his circumcision, and even more so when he begins to learn how to keep the mitzvot. Nevertheless, he is infused with the main component at his bar mitzva, when he becomes obligated by Torah law to observe the commandments.

The completion and the primary infusion of the holy soul into a person [transforming him or her into a complete, adult Jew], occurs at thirteen years and one day for a male, and at twelve for a female, and therefore from that time they are obligated by Torah law to observe the commandments, and become liable for punishment for their sins. This holy soul begins to be infused [in the body] when one is educated [at a young age] how to keep the Torah and its commandments, an obligation imposed by the Sages [upon the parents]. (Rabbi Shneur Zalman of Liadi, Shulĥan Arukh HaRav, Mahadura Batra 4:2)