Oliver's behavior and hints about his parentage tell us that he has an aristocratic heritage.
Foreshadowing is a hint that an author gives the reader at later events in a book. Authors use it to create suspense and to weave a story together.
When Oliver escapes from the undertaker in the beginning of the book, it foreshadows the fact that he is incorruptible.
For a long time, Oliver remained motionless in this attitude. The candle was burning low in the socket when he rose to his feet. Having gazed cautiously round him, and listened intently, he gently undid the fastenings of the door, and looked abroad. (Ch. 7)
Throughout the story, several incidents and people will try to corrupt Oliver, but he never changes his good and gentle nature. This is why the story is a “progress” as the subtitle suggests. Oliver will go through his story but never change. He will remain good, despite the evil he encounters. This is partly, perhaps, because of his upbringing. He is simply not like the lowlifes he encounters. He is an aristocrat just trying to get home, even if he doesn't know it.
One of the evil characters he encounters is Bill Sikes. His character is introduced to us early on as being violent. It foreshadows his killing of Nancy. He is violent when talking to Fagin.
'I wonder they don't murder you! I would if I was them. If I'd been your 'prentice, I'd have done it long ago, and--no, I couldn't have sold you afterwards, for you're fit for nothing but keeping as a curiousity of ugliness in a glass bottle… (Ch. 13)
Sikes’s description, and his abuse of Nancy and treatment of Oliver foreshadows his eventual murder of her. Conversely, her gentle nature foreshadows her helping him.
The fact that Oliver is born with no father’s name given, and with his mother’s name not known, foreshadows his important parentage. Another example of foreshadowing is when Monks and Fagin discuss Oliver’s future. Monks asks Fagin why he wasn’t able to turn Oliver into a pickpocket like the rest of his gang.
'I tell you again, it was badly planned. Why not have kept him here among the rest, and made a sneaking, snivelling pickpocket of him at once?' (Ch. 26)
This foreshadows later information that Oliver has an aristocratic upbringing that Fagin and Monks, who is his half-brother, are trying to keep from becoming known. It is not revealed until the locket from his mother is shown later, with Oliver’s mother’s name.
Fagin was unable to turn Oliver into a thief like the other boys because he isn't like the other boys. He comes from a higher class. He also has a genuinely good nature at heart, and refuses to allow himself to be corrupted.
Throughout the book, Dickens allows the reader hints at what is to happen later. Oliver goes through his story with one bad thing happening to him after another, but he never seems to lose heart. He remains a good-natured soul, un-corrupted and sweet, until he finally finds his way home to Brownlow and learns the truth about his family.