This quote is from the conference Existentialism is a Humanism where Sartre defines his views on existentialism. We shall not repeat the context of this conference, but will try to determine what is his definition of existentialism.
“Start from subjectivity” according to Sartre
Start from subjectivity is the common point of all the existentialist philosophers, whatever their branch. Indeed, Sartre distinguishes between two kinds of existentialism: Christian for Pascal and Kierkegaard, and atheist, like Heidegger or hers.
The man is defined in negative terms for Sartre, as opposed to what he is not: thus, an ashtray has been designed for a specific function, predetermined. The essence of the ashtray live before its existence.
The same thing happens if we consider God as the creator of the universe. If the concept of man is in the mind of God, man becomes an ashtray, that is to say an object, not a subject. That’s why, for Sartre, God does not exist, God cannot exist beacause it would ruin the human life. Because the existence would mean that man has an essence, so is not free, nor responsible for his actions:
“The man first exists, occurs, arises in the world, and it is defined after […] The man is nothing, he will then, and he will be such that it will be done. So there is not likely, since there is no God to conceive”
[Note: We will devote a post to the bad faith and the spirit of seriousness which are to raise the gasoline before the existence]
Sartre, subjectivity and responsibility
For Sartre, Existentialism is a philosophical movement that brings out the subjectivity. The consequence of this principle is that man is totally responsible for his choices and his entire existence. Beyond that, the man is responsible for all men. Because by choosing a man chooses a model of humanity, he poses as an example for all humanity: to choose, engage humanity (“in choosing me, I choose the man”)
Sartre, anguish and anxiety
How the man feels this choice and the responsibility it entails? In anguish. The man chosen ahead of all other men. The man always chooses the midst of an infinity of possibilities, and choose a possible rather than another generates the anxiety of freedom. However, this fear should not prevent the man to choose to act, it is even a condition of action. For it is this fear that gives value to a choice. It confirms that this choice is my choice.
In this place that existence precedes essence means giving power to the man to give him the keys to his fate, a sine qua non of any humanistic philosophy.