Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
Third-Person Limited Omniscient (Mostly)
The majority of the novel is from Tom's perspective and in Tom's "present." That is, we experience events when Tom does and we get the same information as Tom at the same time as he does. The narration straightforwardly conveys Tom's thoughts to us, which makes us feel like we're getting a genuine view of his character. There's no sense that the narrator is withholding, lying, or tricking us. This bluntness can be humorous. Take the following example:
Mr. Vance [the undertaker] was not talkative. He took big bites from his sandwich and was done with the first before Tom was halfway through his own, and finishing his fourth when Tom was only starting in on his third. [….] Tom thought that dealing so much with dead persons must cause a man to have an appetite for food. (24.7)
It can also be poignant:
He had begun milking when Polly Ann came in, her cheeks bright from the cold, and he saw suddenly that she was a pretty woman, as Erlo Ackerman had remembered her being as a girl. Right then he knew that taking out the full two dollars and a quarter [for Christmas gifts] was the right thing to do. (10.20)
Whether the effect is funny (dealing with dead bodies = yum, sandwiches?) or sentimental (my mom's so pretty), we always get the sense that it's Tom's view in earnest.
While we're usually peeping through Tom's perspective, there are times when the narration zooms out of the present moment or out of Tom's point of view. This happens for the whole first chapter when we get the backstory on the Breens, the Hannaberrys, and Nob Dolan, but it happens occasionally even once we get into Tom's point of view.
For an example of a shift out of the "present," take a look at this line:
Time came later, when, remembering those afternoons, Tom thought they must have been the happiest time in Birdy's life. (43.2)
And here's an example of a shift away from Tom's perspective to someone else's:
[Birdy] had gone back to the mow floor. He stood in the middle of it looking up at the timbers, back together in their proper shape, the way he had helped fix them in the first place. A long time, that was. He wondered what Bert Breen would think to see them down here. Or Amelie, either.
Then he saw Tom and Mr. Hook approaching him, and he came down the ladder. (48.6-7)
These shifts into the third-person omniscient (versus third-person limited, with a window only into Tom's thoughts) make us feel like we are watching Tom's life from afar and gaining a bigger picture than Tom has access to. That doesn't necessarily make us feel less connected to him. In fact, it kind of endears him to us more because it shows us that Tom is doing his best to carve out his spot in a wide world.