" unforgiving spirit is not only Satan’s widest door into our hearts, but it is the strongest imitation and warmest welcome. St. Paul not only urges a spirit of forgiveness as a bar to the devil’s ingress, but hastens to close the door by his own readiness to forgive even in advance. “To whom ye forgive anything, I forgive also; for if I forgave anything, to whom I forgave it, for your sakes forgave I it in the person of Christ. Lest Satan should get an advantage of us; for we are not ignorant of his devices.” A lofty spirit, ready and compliant with the spirit of forgiveness, free from all bitterness, revenge or retaliation, has freed itself from the conditions which invite Satan, and has effectually locked and barred his entrance. The readiest way to keep Satan out is to keep the spirit of forgiveness in. The devil is never deeper in hell nor farther removed from us than when we can pray, “Father, forgive them; they know not what they do. "

― E.M. Bounds , Satan: His Personality, Power and Overthrow