The self here is not a cosmic, divine Self, but an individual self.
Intelligence, ego, and the mind are all part of the material world.
These evolutes of the material world arise in succession from the proximity of prakriti and purusha.
By contrast, purusha is unconnected with prakriti. It is pure consciousness, independent of experience.
Purusha is not made up of the three guna, but is an indifferent spectator, the one who sees. Purusha exists outside of the material world in order to offer the possibility of freedom and release. The doctrine assumes a plurality of purushas.
The purpose of Samkhya is to eliminate dukha, the suffering that characterizes human existence in the world.