Private individuals with their own cases are of three kinds. First, there are those who seek vengeance and judgment from the representatives of God, and of these there is now a very great number. Paul tolerates such people, but he dos not approve of them [...]. Nevertheless such will not enter the kingdom of heaven unless they have changed for the better by forsaking things that are merely lawful and pursuing those that are helpful. For that passion for one's own advantage must be destroyed.

In the second class are those who do not desire vengeance. On the other hand, in accordance with the Gospel [Matt. 5:40], to those who would take their coats, they are prepared to give their cloaks as well, and they do not resist any evil. [...]

In the third class are those who in persuasion are like the second type just mentioned, but are not like them in practice. They are the ones who demand back their own property or seek punishment to be meted out, not because they seek their own advantage, but through the punishment and restoration of their own things they seek the betterment of the one who has stolen or offended. They discern that the offender cannot be improved without punishment. These are called "zealots" and the Scriptures praise them. But no one ought to attempt this unless he is mature and highly experienced in the second class just mentioned, lest he mistake wrath for zeal and be convicted of doing from anger and impatience that which he believes he is doing from love of justice.

-- Martin Luther in a sermon on the "two kinds of righteousness", likely delivered in 1519. Quoted from John Dillenberger's Martin Luther: Selections from His Writings, 94-5. Emphasis is mine.