Edith Stein

Today is the feast of St. Teresa Benedicta a Cruce, more commonly known as St. Edith Stein. Raised an atheist in a secular Jewish family, she studied philosophy under Husserl and was baptized into the Catholic Church on January 1, 1922. She taught at a girl's school until she was forced to resign by anti-Jewish laws put into effect by the Nazis. She then became a Discalced Carmelite in 1934. She and her sister, also a convert, were eventually sent to a monastery in the Netherlands in the hopes of protecting them, but the Nazis invaded shortly thereafter. And on August 2, 1940, she and her sister were among a large number of Catholic Jews in the Netherlands who were rounded up by the Nazis in retaliation for Dutch Catholic policies, and they were sent to Auschwitz. We don't know precise details from there, but she is thought to have died in the gas chamber on August 9. She was canonized in 1998 by St. John Paul II.

From her work Potency and Act, which she wrote as a thesis in 1931 but which was not published until after her death:

Genera and species prescribe beforehand a framework that abides throughout the individual's entire duration in being and is concretely fulfilled successively by variable [veränderlich] accidents. We should then take substance here (in the sense of "second substance") as an instantiated general species. It becomes a concrete individual by being successively filled, and for the first time actual being accrues to the concrete individual--with its abiding stock as well as its changing stock.

Actuality cannot be due either to the abiding stock, or to the changing stock, or to the form of the individual; for each of these "abstract parts" of the concrete individual requires the others, nor can the individual being bring them about or draw them into itself. Thus all mutable being, all becoming, points to an upholding outside of itself, to something immutable, to absolutely actual being. What becomes must take its origin [Ursprung] from what is immutably and thereby it must be upheld.

[Edith Stein, Potency and Act, Redmond, tr., Gelber and Leuven, eds. ICS Publications (Washington, DC: 2009) p. 70.]