Nature and Grace by Thomas Aquinas. Thomas Aquinas was born in 1225, he was an Italian priest of the Catholic Church in the Dominican Order, and an immensely influential philosopher and theologian in the tradition of scholasticism, known as Doctor Angelicus (the Angelic Doctor) and Doctor Communis or Doctor Universalis (the Common or Universal Doctor).
Here is his work “Nature and Grace: Selections from the Summa Theologica of Thomas Aquinas” in full text for your download pleasure (1,5 MB, 335 pages):