After age thirteen, a person’s performance of mitzvot – performed with the intention to give satisfaction to his Maker – begins purifying the selfish desire to receive that had been imprinted in him. [Performance of mitzvot] gradually turns [that selfish desire] into a desire to give. This gradually draws [mamshikh] the holy soul from its roots in the plan of creation. It [the holy soul] traverses the entire system of sanctified worlds and becomes enclothed in the body. That is the time of repair.
What Happens to the Soul at Age Thirteen
Baal HaSulam's Introduction to Zohar 11:2