The concept of Dual (or double or yin/yang) is a prevalent concept in Taoist thinking. In Tao Te Ching chapter 42, it says (my translation):
In the beginning
Tao comes to beget one
One develops into Two opposites
While Two breeds the possibility of a reunification
and Three being the nature of everything.
Hence everything consists of both Yin and Yang
and when facilitated by Essence
they will be combined together as one....
In actual meditative practice, it is the reunification of yin and yang to reach back to Tao. A kind of reverse drive.
Concerning the objectives of the practice, there are indeed two: Life and Death. What is the Life objective? It is a personality change. For the most devoted it would be turning into a "worldly Immortal", not in the sense that he or she won't die, but in the sense of he or she is saintly selfless, similar to a Bodhisattva in Buddhism. Although in practical terms, it is more like an ideal for most people, it can be (and is being used as) an objective towards which a practitioner tries to achieve. In modern terminology, the objective will be like becoming a better person. Or simply to have a higher EQ!
Some of my readers may think that this objective is common place, or nothing new, not profound enough as a life objective. Wait until next time when you talk to a "spiritual person" over the internet or face to face and notice how he changes his face when you disagree with him on some issues during your discussion!
How about the Death objective? It is a preparation for death. Why we need to prepare for death? Because we can't put down our "images" of worldly possession. If one can lay down such "false attachment", one will welcome the joining with Tao with a calm mind (unlike modern populist spiritualism, happiness is NOT assumed here - happiness, like sadness, is still an attachment in high-level Taoist thinking). According to "Taoist yoga" of Zhao BiChen (趙壁塵), a devoted Taoist should not practice the highest level of joining with Tao too early (he was referring to the second objective here). First he should raise up his kids who would then be able to take care of his spouse (their mother), and then he had to wait until his parents were passed away, and he should have retired too. With no worldly attachment, he could "freely" go into the practice with the ultimate objective of preparation for death (or Immortality). If a modern reader is still skeptical about my exposition of this second Taoist objective, he should refer to the commentary written by Carl Jung in Wilhelm's Secret of the Golden Flowers, a seminal Taoist text. Jung drew the same conclusion there.