Our spirit is our first estate. When Lucifer rebelled against God, he lost his first estate and was cast down to earth along with one third of the hosts of heaven, of whom, decided to follow his plan.
We, on the other, after obtaining our first estate came to earth to receive our second estate (body of flesh and bone) to dwell here and follow the plan of God.
When we die, as an intelligence housed with a spirit and body, will go forward and be in our third estate, meaning we have kept the other two to never be divided ever again.
Cain will rule over Lucifer due to the fact that Cain has a body and Lucifer does not.
Moses 5
23 If thou doest well, thou shalt be accepted. And if thou doest not well, sin lieth at the door, and Satan desireth to have thee; and except thou shalt hearken unto my commandments, I will deliver thee up, and it shall be unto thee according to his desire. And thou shalt rule over him;
24 For from this time forth thou shalt be the father of his lies; thou shalt be called Perdition; for thou wast also before the world.
Moses 5:30
30 And Satan sware unto Cain that he would do according to his commands. And all these things were done in secret.