the relationship between existentialism and essence

Existentialism holds that the existence of human beings is meaningless, and that the meaning of human existence is endowed by itself, not belief, god, science, reason, morality and so on.
The essence is the form that exists. In other words, existence is the existence of physics, and the essence is the meaning of existence. Before it existed, the object was not given any meaning by anything.
This novel is a good illustration of the relationship between the two. Before the war, there were many animals in the world, and their existence was very common. But after the war, the animals began to die out, and once they were so common that they became so precious that the animals became a symbol of social status, and the more cherished the animal is, the more it represents the status of the possessor, and those who cannot afford it will be looked down upon. At this time, animals are still animals, and their existence has not changed, but the meaning of their existence, which is the essence, has changed. They are endowed with new meaning by human beings, and their essence is no longer the life of an individual, but becomes a luxury which is used by people to satisfy their vanity. In this novel, Rick had a fake sheep, but he has been eager to have a real sheep, because of the fake existence of the fake sheep, will one day be people see through, but not really a sheep. On the other hand, in essence, both the meaning of real sheep and fake sheep exists to satisfy rick's vanity, so there is no difference between the two. Thus, through this example in the novel, we can conclude that existence precedes essence.