The dragon Eustace– When Eustace was a dragon and tried to scratch his scales off so as to bathe in the bath, he couldn’t do it and it kept on coming back until Aslan helped him. This parallels how we can’t forgive our sins without Jesus. We can try, but it always comes back. We need what he did on the Cross for us to remove our sins so that we may one day be in Heaven with him.
Lamb found on shore by Aslan’s Country– I think this The Lamb of God. This is one of Jesus’s names. John 1:36
The Dark Island– The man who came off the Dark Island said to never take him back there. When they look back, the island has disappeared. This is like when we really don’t want to have sin in our life and we ask for forgiveness, our sin disappears. They are removed from us as far as the East is from the West. Luke 5:20