Saint Augustine says the following, which strikes me as very true:
This law, Eye for eye, tooth for tooth, was enacted to repress the flames of mutual hate, and to be a check on their undisciplined spirits. For who when he would take revenge, was ever content to return just so much harm as he had received? Do we not see men who have suffered some trifling hurt, straightway plot murder, thirst for blood, and hardly find evil enough that they can do to their enemies for the satisfying of their rage? To this immeasured and cruel fury the Law puts bounds when it enacts a lex talionis; that is, that whatever wrong or hurt any man has done to another, he should suffer just the same in return. This is not to encourage but to check rage; for it does not rekindle what was extinguished, but hinders the flames already kindled from further spread. It enacts a just retaliation, properly due to him who has suffered the wrong. But that mercy forgives any debt, does not make it unjust that payment had been sought. Since then he sins who seeks an unmeasured vengeance, but he does not sin who desires only a just one; he is therefore further from sin who seeks no retribution at all. I might state it yet thus: It was said to them of old time, You shall not take unequal retaliation; But I say to you, You shall not retaliate; this is a completion of the Law, if in these words something is added to the Law which was wanting to it; yea, rather that which the Law sought to do, namely, to put an end to unequal revenge, is more safely secured when there is no revenge at all.
. . .
For the righteousness of the Pharisees is a less righteousness, not to transgress the measure of equal retribution; and this is the beginning of peace; but perfect peace is to refuse all such retribution. Between that first manner then, which was not according to the Law, to wit, that a greater evil should be returned for a less, and this which the Lord enjoins to make His disciples perfect, to wit, that no evil should be returned for evil, a middle place is held by this, that an equal evil should be returned, which was thus the passage from extremist discord to extremist peace. Whoso then first does evil to another departs furthest from righteousness; and who does not first do any wrong, but when wronged repays with a heavier wrong, has departed somewhat from extreme injustice; he who repays only what he has received, gives up yet something more, for it were but strict right that he whom is the first aggressor should receive a greater hurt than he inflicted. This righteousness thus partly begun, He perfects, who is come to fulfill the Law.
