Jesus tightly links our relationship with God to our relationship with others. It works two ways. If we have not seen our sin and sought radical forgiveness from God, we will be unable to forgive and to seek the good of those who have wronged us. So unresolved bitterness is a sign that we are not right with God. It also means that if we are holding a grudge, we should see the hypocrisy of seeking forgiveness from God for sins of our own. Calvin puts it vividly: