Eternity also means all the time before you were born as well. It is difficult for the human mind to grasp the idea of eternity. Often people think eternity starts after they pass away out of the body, or die. No. Eternity is everything before we were born into these bodies as well.
Not every soul incarnates at the same time. Many stay in Pure Positive Energy (what some call heaven) until the setting is right for their next incarnation. This depends on the unique growth needs for that soul.
Our souls are like rays of the sun—they all originate with the sun and cannot exist without the sun, yet each is an individual. As for the point of it all that is something each person must discover, for each soul is on its own journey and will eventually return to its Source.