Plantinga writes in this chapter about the redemption of man. He starts off the article with “human misery is nearly as old as the human race, but equally old is the story of God’s grace, that is, God’s mercy to the undeserving.” He is saying that we are undeserving of anything that God gives us that we should have nothing on this earth, but by the grace of God we are supplied with our daily bread.
He then goes on to talk about all of the nice pleasures that we as humans had when God called us into His fellowship before the fall. The redemption that Plantinga is talking about is something that has come out of necessity because of the fall.
Christ went to the cross to pay for the original sin of the fall and because of the resurrection of Christ we are saved from the torments of hell. We deserve hell but because of the death on the cross we are saved.