Shalom, The sage advice the torah gives is to not be "makpeed" or insistent on ones rights and by extension vengeance or revenge is something that is forbidden. In terms of the biblical story of the sons of Yakov avinu wiping out Shechem there is a seeming contradiction for this. Actually there is a deeper layer of meaning here which the "purely textual" analysis will not reveal. We can say for our intents and purposes that revenge is not advised by the torah. Taking Revenge or Nekama is clearly forbidden in our age. There was the concept of a "goel Dam" blood avenger who would have special circumstances connected to his situation that would allow vengeance...but again this is not a concept that applies today. --R.Yosef Karpman