God's Forgiveness is necessary for salvation and His favor to you. 

Man's Forgiveness of others is necessary for one's own health and to release others to receive God's favor.

Self Forgiveness is also necessary for one's own health spiritually, mentally, and physically.

To Love the Lord with heart, mind and soul and strenght, and one's neighbor as one's self is to have experienced forgiveness and to have forgiven others as well as self.  (The Lords Prayer Matt. 6:12)