Medieval Period
Augustine of Hippo
Hamartiology
Augustine's view of original sin and grace was influenced by early religious experience and anti-Pelagianism. But the main concept still comes from his research on The Book of Romans. He believes that even if a man has not fallen, the future destiny of man still has to depend entirely on the decision of God.
Resource from https://zh.wikipedia.org/wiki/%E5%B8%8C%E6%B3%A2%E7%9A%84%E5%A5%A5%E5%8F%A4%E6%96%AF%E4%B8%81#%E6%95%91%E6%81%A9%E8%AB%96
St Thomas Aquinas
Hamartiology
Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of right and wrong behavior."The field of ethics, along with aesthetics, concerns matters of value, and thus comprises the branch of philosophy called axiology. Ethics seeks to resolve questions of human morality by defining concepts such as good and evil, right and wrong, virtue and vice, justice, and crime. As a field of intellectual inquiry, moral philosophy also is related to the fields of moral psychology, descriptive ethics, and value theory.
Resource from https://en.wikipedia.org/wiki/Ethics
Marco Orillo
Meditations
Meditations (Medieval Greek: Τὰ εἰς ἑαυτόν, romanized: Ta is heauton, literally "things to one's self") is a series of personal writings by Marcus Aurelius, Roman Emperor from 161 to 180 AD, recording his private notes to himself and ideas on Stoic philosophy.
Marcus Aurelius wrote the 12 books of the Meditations in Koine Greek as a source for his own guidance and self-improvement. It is possible that large portions of the work were written at Sirmium, where he spent much time planning military campaigns from 170 to 180. Some of it was written while he was positioned at Aquincum on campaign in Pannonia because internal notes tell us that the first book was written when he was campaigning against the Quadi on the river Granola (modern-day Hron) and the second book was written at Carnuntum.
It is unlikely that Marcus Aurelius ever intended the writings to be published and the work has no official title, so "Meditations" is one of several titles commonly assigned to the collection. These writings take the form of quotations varying in length from one sentence to long paragraphs.
Resource from https://en.wikipedia.org/wiki/Meditations