First person narrators

Gabriel Rosenstock was on Miriam Meets this morning. This Sunday morning meditation is an interview with two people who are connected by love or friendship or family relationship, or, often, all three.
They talked about how the family came to be - a German doctor met a Galway woman in Jersey when he was in the Wehrmacht; his friends broke his arm to save him from being posted to the Russian front; they returned to Ireland where he set up a practice allied with a chemist's shop so he could import pharmaceuticals from Germany - funny enough, the same plan my grandfather had for my father, then a medical student, and his brother, a plan nuked when my father had a highly-praised student production of Eliot's Murder in the Cathedral and took to the stage.
They talked about the family poker games, played for real money, money that was lost and won and kept by the winner, even when the loser was 13-year-old Mario, losing £90 of the £130 he'd won the night before, a good lesson for a young gambler.
And then Gabriel started talking about reality. In a particularly hideous twist of fate, his uncle had been drowned while a schoolboy in Clongowes, and then his brother was drowned at 17 in Glendalough - it's possible, apparently, that his friends dared him to swim across one of the lakes, which look so narrow between their steep mountain sides, but are so horribly wide and cold.
Curiously, Marian did not ask him about the horror of the two successive drownings of athletic boys in two generations of the family. What she did ask him, from her own pain at the loss of her sister, was about the effect. Gabriel was dismissive of any idea of division from his brother - he was 10 when his brother died, and the death broke his parents' marriage. You are not born, he explained, and so you do not die. His brother - the essence of him, not his age or sex or nationality or intelligence or anything that we consider makes a person himself, but rather the essential core of that person - is still here, he said.
Marian said, in a voice that sounded so bereft: "But you can't touch him", and she leaned to touch Gabriel's hand. All the people living all alone now turned their faces from the radio.
When you write in the first person, you're mining the essential core that Gabriel Rosenstock was talking about. Your character (for some writers always a version of themselves - come to think of it, Jungians would say that for all writers each character is a version of themselves, because they are its creator) may be an observer, like Scout in To Kill a Mockingbird, who sees the action played out from the sidelines, while her growing-up is a subplot reflecting that main action. Or they may be the centre of the story, like Holden Caulfield in The Catcher in the Rye, whose disillusionment and rejection of his upper-class American world is the story.
But in every case, narration in the first person is heavy in subtext. Everything the narrator says has two purposes: to tell the story, and to tell the reader about the person who's telling the story. When Scout observes her father Atticus take off his glasses, draw a measured bead, and shoot dead the rabid dog, she does so from the viewpoint of a thrilled child discovering that her dull old dad is a hero. She's also prefiguring the later action when Atticus shows himself as a true hero, defending humanity. And the lemony regret that underlies her telling is a taste of the failure of that decency, because the man and the values her father defends will die at the end of the book.
In Holden's anger at the phoniness of his society, there is another subtext: Holden has only one spoilt choice in the end - no matter what he does, he is going to become part of his class, the class he hates and derides.
All this sounds mechanical; but a lot of the time a writer is bumbling along telling the story, becoming that core - whatever Gabriel says, we are all myriad people - and knowing nothing about the subtext that's writing itself without the writer realising.