Prison isn't supposed to be about getting revenge, that's nonsense.
Revenge:
"the action of hurting or harming someone in return for an injury or wrong suffered at their hands."
Some may argue that imprisonment is harming somone, i'd argue that it only becomes that once you put people in solitary confinement and don't give them their basic human needs.
I have no issue in a society that if you murder somone by slicing their throat open with a knife, you are required to spend the rest of your mortal life locked away from society, and even if you have truly atoned for your sins and are no longer a threat to society then you can earn more privledges and move towards a prison facility that allows more freedoms. But you should serve your time as a punishment for taking that life.