Forgiveness is not something that is impossible for man. Jesus spoke many times about the necessity of forgiving others. With respect to this, you may remember the parable of the unmerciful servant. The servant was in great debt (10,000 bags of gold) to his master and sought forgiveness and mercy from the debt. The master obliged out of kindness and sent the servant away, after which the servant came across another whom was indebted to him to the amount of 100 gold pieces. The servant was asked for mercy and forgiveness, but showed none. After the master found out, the first servant was thrown into prison until the original debt could be paid.
Jesus was making a couple of stellar points:
-First, we have a specific responsibility to forgive just as we were forgiven; perhaps this is solely by the power of the Holy Spirit, but it is a action we are responsible for performing.
-Second, by contrast, our debt was so much more than anything anyone could ever do to us. For this, we have a great responsibility to be merciful and forgiving, for great is the forgiveness which was given to us.
As hard as it can be sometimes, we have an important command to forgive as we have been forgiven.