The answers are: theological concerns and sin and retribution.
During the middle ages, most knowledge production was centered on monasteries, universities, or the Church and the most common subjects studied were theological in nature. Theological matters deal with the study of the nature of God and humanity´s role in relation to him. It was only natural that these studies would consider the analysis of sin and retribution as an important topic, often treating these as parts of ethical or moral arguments based on virtue and vice. One good example of these kinds of texts can be found in Dante´s Inferno or in Aquinas´ Summa Theologiae.