Avodah Zarah 5: Repentance Leaves Sin in the Dust

On sin and the purpose of sin! God allows sin to happen so that future sinners can repent. Consider the story of King David with Batsheva, with the implication that David wouldn't have done the sin were it not for his later repentance. Comparably, the sin of the Golden Calf. When an individual sin, we encourage reflection, repentance, and atonement. A group sin is a little more complicated, but the same principle stands. Plus, the differences between humans and angels, including, or especially, progeny. Plus, the harsh punishments for sin (for example, Rabbi Akiva). Also, a return to halakhah, with the question of why 3 days of not selling to non-Jews before their holidays (why not more or less)?