The binding of the adversary is the mastering of the lower drive within a person. The dragon is the reptilian force at the base of the body, the coiled sense-energy that deceives the mind while it rules. Cast down and sealed in the bottomless pit, it is driven back into the deep unconscious below waking sight, shut away so it can no longer mislead the many faculties of the self.
The number 1000 stands for a completed round of spiritual rest, a long interval in which the higher awareness governs unopposed. That the beast is loosed a little season afterward shows the old energy is subdued, not destroyed: mastery holds for a full cycle, then the base force must be met and overcome once more.
Dragon: the coiled reptilian sense-energy at the base of the body, deceiving the mind while it goes unmastered.
Bottomless pit: the deep unconscious beneath waking sight, where the subdued lower drive is sealed away.
Thousand years: a completed cycle of inner rest in which the higher awareness reigns unopposed.