Please explain why Nick Carraway says he's "inclined to reserve all judgments."

Nick begins narrating his recollection of his Gatsby story, by describing himself as being “inclined to reserve all judgments” as a reminder, both to himself, and the reader that the best choice is tolerance according to what his father taught him. The author or the story, F. Scott Fitzgerald, brilliantly introduces his narrator by allowing him to reveal this trait so naively to the reader only after he has said that he followed this advice in his “younger and more vulnerable years.” In doing so, he creates a story told by a character who the reader can rely on to be unbiased, or at least to try. In further contemplation of Nick’s character, the reader begins to wonder if the trait of not “judging” could possibly cause events and people to come crashing down. Also, Nick really does not say that he doesn’t judge. He says that he is “inclined” not to judge, possibly a somewhat less-admirable quality. He continues to describe his talent of tolerating others as giving him an “infinite hope” and an ability to recognize all of those who haven’t had it as good as he has. Ironically, this very talent for not getting involved may impair his ability to judge his own actions in the story. The purpose of Nick’s saying that he’s “inclined to reserve all judgments” sets up the expectation that he will narrate the story with compassion and objectivity. But at the same time, the reader must consider that his recollection of what happens in his Gatsby story may come from a bleak and indifferent perspective.

In the third paragraph of the novel, Nick Carraway states that he's "inclined to reserve all judgments." In other words, he is saying that when people talk to him, he tends to listen quietly and not say what he thinks. He explains that because of this personality trait, people often open up to him and tell him secrets that they would not normally tell other people.
Nick is the classic observer: he is the type of person who stands on the edge of a scene, watching what other people are doing. He is a good listener rather than a talker.
Nick does judge, calling people "bores" and saying they often lie by omitting parts of their stories (what he calls "obvious suppressions") and saying that he has to remind himself of his father's words, that everybody isn't born with the same advantages.
Although Nick does judge, he keeps quiet about his feelings and doesn't openly criticize others. Therefore, because he seems safe, people tell him things.
Nick is explaining how he knows so much of the Gatsby-Buchanan saga, even though he was primarily an outsider looking in.