The episode set the pattern of focusing on one character and telling their earlier story in flashbacks. The irony is that the title means “clean slate,” and yet the flashbacks show things that shape who characters are, even on the island. Jack says that it doesn’t matter who we were before, and says, “Three days ago we all died. We should all be able to start over.” This was intended to get people wondering whether these are survivors, or people in purgatory.
It also started to hint at the importance of John Locke’s character, both when we learn that he experienced a miracle, and by the eerie music and focus on him in the final shot.
Baptism is a well-known symbol of death and rebirth, and lots of religions have used similar imagery. Coming to the island is depicted from the beginning as akin to a religious experience – and in this episode, there is the specifically Christian echo of “three days.”