Where does the Bible say that those who forgive will be granted everlasting life?
Matthew 18:21-22 recounts Christ telling Peter that he must continually (“seventy times seven times”) forgive those who have wronged him. In the parable of the unforgiving debtor (Mt 18:23-35), our Lord proceeds to point out that God will deal with us mercifully only if we in turn will deal likewise with one another and states that God will deal harshly with us if we do not extend that forgiveness to others.
So it is clear that God demands men forgive one another; not only that, but that men actively seek forgiveness from each other. It is also clear that human forgiveness, both in seeking and in granting, is an integral part of human participation in the divine life of grace and therefore of salvation itself.