Abraham Lincoln talks about the sacred ground at Gettysburg. In Remember the Titans the coach reminds them of the battle fought there 100 years ago. Blood spilled makes the ground holy. That is why Christians revere the Cross - Christ' blood there makes that holy ground.
Any relationship that is un-bled is un-redeemed. If you are really going to love someone, open your heart to them - you are going to get hurt. When we chose to forgive for His sake - He uses that opportunity to forgive and redeem that relationship.
Choosing forgiveness for Christ' sake is the means by which God purchases areas in our lives for His glory. When we forgive the Blood of Christ flows through our wounded hearts onto the ground of that relationship or area and Satan and his demons will not walk over a ground where the Blood of the Christ is.