Romans

Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written(see Deuteronomy 32:35), Vengeance is mine; I will repay, saith the Lord.

Paul is saying a person should not take revenge, but instead, allow God to judge them. All sins must be paid, if you are in the old covenant(which you are not) God tells one to do sacrifice(read Leviticus for more). If you are in the new covenant, Jesus' payment on the cross can subdue God's vengeance. If one does not accept Jesus, then the person must pay for their crime in Sheol. An unfun place indeed.