עמוס א:ג קבלה: Assarah Perakim L'Ramchal

What is reincarnation and what is intercalation? Reincarnation is from the moment of birth to the moment of death; intercalation can come every "hour", and can leave every "hour". A mitzvah in which the soul is obligated to fulfill happens in a reincarnation, and one that the soul is not obligated to fulfill happens in an intercalation, from the moment is is fulfilled it [the intercalation] is gone. Righteous [people/souls] can reincarnate a thousand [times], evil [people/souls] up to four, as it is written "and to the fourth I will not make her return"(Amos 1:3).