From the book's very first sentence, a character's way of using language gives us clues to their educational level, what kind of background they come from, and, to some extent, where they are on the social scale.
Let's take a look at that first sentence: "I should of been in school that April day" (1.1). Now Shmoop knows, and Shmoop knows that you know, that the grammatically correct way of saying that is actually, "I should have been in school." So the fact that our narrator doesn't write it the "right" way immediately gives us some insider knowledge about him. He's a colloquial, informal kind of guy who's not too concerned with (or aware of) the rules of grammar.
In contrast, the one more educated character whose voice we hear in the book, Aunt Matty—who we're told once taught English—uses language in a much more formal way than most of the other characters, just as you would expect her to. Is she a fancypants intellectual? Maybe not. But it's all about how the characters look relative to each other. And if anyone's the snob in this situation, it's Aunt Matty.
Since the story comes to us by way of a first person narrator, we get to share a lot of Rob's ideas and opinions in the course of the book. He tells us how he feels about the other characters, his thoughts about things that they say, and his wishes for the future. Example? Why, sure. Soon after Mr. Tanner gives him his new piglet, Rob pauses to tell us about her.
Looking at her again, I could now see how beautiful she was. My pig. She was prettier than Apron, or either one of her calves. She was prettier than Solomon, our ox. Prettier than Daisy, our milk cow. Prettier than any dog or cat or chicken or fish in the whole township of Learning, Vermont. She was clean white all over, with just enough pink to be sweet as candy. (3.51)
It's pretty direct way of allowing us to get to know Rob. He tells us what he thinks… the end.
Remember how Papa takes such good care of his tools? What does that tell you? For us, we get the feeling that he puts a lot of stock in hard work and in his responsibility to care for his belongings.
Even the way Papa kills pigs is distinctive: "When you kill pork and twain it, head to rump," Rob tells him, "you always do what no other man does. You even divide the tail, and half it right to the end" (12.64). This trademark way of butchering proves how dedicated Papa is to doing things right, right down to the last detail.
And Papa's not the only one. Mr. Tanner's habits of punctuality, cleanliness, and responsibility as the marks of a good farmer: "His fence is straight and white as virtue," Papa tells Rob, "[and] all the critters are clean" (12.51). Bottom line: if you want to be seen as a good person, make sure your fence is straight.