existence before essence

Existence before essence means: people first exist, then make decision. What decision people make determine their essence.
To people, because people need to think of their meaning of living, the meaning of living can be described as the essence. But what before the essence, is the living people. The way to find one thing’s essence, is to observe what it can do, or the ability of this thing. The “thing” here, can be tools, can be people, can also be animals.
For example, a hammer, people observe its shape, and find this is an useful tools. The shape of this hammer is the existence, and the usefulness, is essence. But, without knowing its shape can be used as a tool, how can people learn that the hammer is useful? People is just like this hammer, without knowing the basic ability of people, they will never know their meaning of existence.
Another example is people’s action. It is common knowledge that people can work to get income. But without working, one will not be paid. To think that working is people’s action and the income is the result of their action, which is the meaning of working. Because people work, then their work will be judge about how much their work is deserved. The value of people’s work is the essence while the work is the existence.
In the novel, people decides to move to Mars, this is the decision that people make. Then, they can avoid the environmental pollution of Earth.