The Holy Ari writes in Shaar Hagilgulim that every person who comes to the world comes for the sake of a personal and unique tikkun [rectification], and one person does not resemble another.
Each person have a personal path and way to rectify and to walk for which he came to the world.
Rebbe Natan says:
All our spiritual descents are in order to perform a "redemption of the captives."
This means to redeem the sparks of holiness, which are very lofty spiritual forces that got lost in tumah [spiritual impurity], and in order to bring them back to holiness, we must descend to there.
And then, when a person does teshuvah [repents], he brings them back together with himself.