"The principle was to restrict the scope of revenge." I think rather the principle is one of justice. Lamech is an example of revenge (not justice). Revenge is

"The principle was to restrict the scope of revenge." I think rather the principle is one of justice. Lamech is an example of revenge (not justice). Revenge is never given to men by God ("It is mine to avenge; I will repay"). "But the NT turns completely against that idea." No, not at all, or when last did you read the Bible carefully? Jesus taught plainly that to turn against the words of Moses at all even in the slightest is to turn against Jesus himself. Jesus taught plainly that if you won't accept the words of Moses, you won't accept Jesus' own resurrection from the dead. "the concept of mercy and forgiveness is just not emphasized as much in the OT as it is in the NT." That is a gross misrepresentation of the OT. You've fallen for Marcion's error and worse. With the merciful you show yourself merciful; with the blameless man you show yourself blameless; with the purified you show yourself pure; and with the crooked you make yourself seem tortuous. For you save a humble people, but the haughty eyes you bring down.