Endless becoming

I can't recall what book I jotted this from, but I found it in some notes I was throwing out:

Later in his philosophical development the idea of freedom became Sarte's main theme. Man, beginning in the loathsome emptiness of his existence, creates his essence -- his self, his being -- through his choices that he freely makes. Hence his being is never fixed. He is always becoming, and if it were not for the contingency of death he would never end. Nor would his philosophy. "Existentialists," wrote Irish philosopher Arland Ussher, "have a notable
difficulty in finishing their books: of necessity, for their philosophy --
staying close to the movement of life -- can have no finality."