“Enq: You mean, then, that we have all lived on earth before, in many past incarnations, and shall go on so living?
Theo: I do. The life-cycle, or rather the cycle of conscious life, begins with the separation of the mortal animal-man into sexes, and will end with the close of the last generation of men, in the seventh round and seventh race of mankind. Considering we are only in the fourth round and fifth race, its duration is more easily imagined than expressed.
Enq: And we keep on incarnating in new personalities all the time?
Theo: Most assuredly so; because this life-cycle or period of incarnation may be best compared to human life. As each such life is composed of days of activity separated by nights of sleep or of inaction, so, in the incarnation-cycle, an active life is followed by a Devachanic rest.
Enq: And it is this succession of births that is generally defined as reincarnation?
Theo: Just so. It is only through these births that the perpetual progress of the countless millions of Egos toward final perfection and final rest (as long as was the period of activity) can be achieved.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 