Jean-Paul Sartre, that quintessential French philosopher of the 20th century, pronounced in his famous 1946 lecture “Existentialism is a Humanism” (https://www.marxists.org/reference/archive/sartre/works/exist/sartre.htm) that “Existence precedes essence”.
He argued that we create a knife with a predefined purpose; that is, the knife we bring into existence only after we have conceived the essence of what a knife is or what purpose we have in mind that it will serve.
But he being an atheist, he went on to say that unlike a knife, when it comes to us humans, since there is no God to conceive an essence for us before he creates us, our “Existence precedes essence”.
He opined, “We mean that man first of all exists, encounters himself, surges up in the world – and defines himself afterwards. If man as the existentialist sees him is not definable, it is because to begin with he is nothing. He will not be anything until later, and then he will be what he makes of himself. Thus, there is no human nature, because there is no God to have a conception of it. Man simply is. Not that he is simply what he conceives himself to be, but he is what he wills, and as he conceives himself after already existing – as he wills to be after that leap towards existence. Man is nothing else but that which he makes of himself. That is the first principle of existentialism.”
Now, even without countering Sartre’s claim that God does not exist, we can very quickly dismantle Sartre’s claim of radical freedom that we humans have thus:
The freedom which we exercise is obviously driven with our thinking and reasoning that precedes any choices we make or decisions we take. But such thinking and reasoning depends not only on what kind of brain nature has endowed us with but also, as even Sartre would appreciate, having been a Marxist, the society we are born into shapes the very possibilities and potentialities for such thinking and reasoning. The brain and genes we have no freedom over as to what kind of such entities we give to ourselves, and society anyway precedes our existence.
Thus, Nature fixes the “essence” that each of us has in the form of our genes and brain with which we are born (so, “Essence precedes existence”), and society then restricts in what ways even such a fixed essence can operate or express itself.
Hence, Sartre’s claim that “Existence precedes essence” is untenable even if God does not exist.
Know Thyself 