First we discuss the Old Testament teaching "an eye for an eye and a tooth for a tooth" - explaining why self defense, just war, and even the death penalty are objectively permitted (and that the Church cannot ever change her teaching on these). However, even if objectively permitted, these practices are all dangerous - and we should be cautious about promoting them. Furthermore, it is prudent and wise of the Church to caution against the death penalty, and to teach that the death penalty should not be used in modern society (because modern society has become rather anti-christian and pagan).
Then we consider how the saints have fulfilled these teachings of our Lord to "turn the other cheek" etc. Finally, we see why love of enemies is the key to spiritual perfection.
Listen online [here]!