His forgiveness covers everything and everyone who will accept it.
It is important to repent of sin before partkaing of the Lord's Supper because sin separates us from God.
He referred to the violent nature to show His martyrdom, that He died for us. It probably freaked out the disciples when they first heard it, but later when they understood, they could be comforted (although that seems too weak word), knowing that He had given His life for them.
It is a proclamation in that it is an outward sign of our belief in Christ's death for our salvation. The proclamation is made to anyone who sees it. It is important because it is an active showing of our beliefs. The church becomes dead with this is not the central theme.
Our remembrance of his death is important because that and His resurrection are our source of salvation.
If we neglect remembering in this way, then Christianity is no longer "living." It is dead religion.
Personally, if we forget His death, we become spiritually dead.
The part that is most valuable to me right now is the idea of nourishment and sustenance. That idea gives me great strength, and it's a very cool thing to keep in mind daily.