Dickens is able to engage the reader in the first chapter of Oliver Twist through the depiction of difficulty and struggle that define the protagonist's life.
The dominant element in the first chapter is how Oliver's life was difficult from birth. The level of toughness Oliver needs to simply enter the world engages the reader. Dickens invokes a gritty reality where only the tough can survive. For example, the first paragraph focuses on a workhouse. The profound difficulty of living in the workhouse forces the reader to imagine the fortitude required for mere survival.
Dickens describes the struggle in Oliver's birth: "Now, if, during this brief period, Oliver had been surrounded by careful grandmothers, anxious aunts, experienced nurses, and doctors of profound wisdom, he would most inevitably and indubitably have been killed in no time." The reader is engaged with a character whose act of breathing constituted struggle and necessitated perseverance.
The reader is drawn in until the chapter's conclusion. Oliver is born to a mother who dies, becomes "a parish child—the orphan of a workhouse," and ends up being "despised by all, pitied by none." The reader is hooked because he/she realizes that Oliver's first moments in the world are defined by real struggle. Oliver is the ultimate underdog. It's hard not to find such a narrative compelling. Dickens's opening chapter clearly establishes that life is painfully hard for Oliver and it is only going to get worse. The reader is engaged because they are compelled to see how much more difficult it is going to be and if there can be any redemption for someone who sorely is in need of it.