| Quote #1
But Kynge Pellynore bare the wyte of the dethe of Kynge Lott, wherefore Sir Gawain revenged the deth of hys fadir the tenthe yere aftir he was made knyght, and slew Kynge Pellynore hys owne hondis. (51.24-27)
Even in this moment, when Pellynore's death is still far in the future, our narrator still brings it up. Regardless of whether or not he's some sort of psychic, our narrator's mention of this tells us that this is a pretty important part of the story. This particular blood feud is as much a part of the Round Table's fall as Gwenyvere's affair with Launcelot, so the narrator drops hints, even this early in the story.
| Quote #2
"Alas!" seyde the knyght, "I am slayne undir youre conduyte with a knyght called Garlonde. Therefore take my horse, that is bettir than youres, and ryde to the damesell and folow the queste that I was in as she woll lede you – and revenge my deth whan ye may." (53.16-20)
By promising safe conduct to this knight, Balyn was, in effect, vowing to lay his body on the line for him. Since he has failed to do that, he now really owes it to the guy to risk his life in a battle for vengeance with the knight's killer. And he barely even knows the guy.
| Quote #3
And on the morne they founde letters of golde wretyn, how that Sir Gawain shall revenge his fadirs deth on Kynge Pellynore. (54.5-8)
Well this is odd. Balyn has just erected a tomb for yet another knight killed by this Garlonde fellow. But instead of the inscription telling that story, the tomb predicts the future – Gawain's revenge on Pellynore. It's a moment of foreshadowing, so that when Gawain does take his revenge, we're forced to look back on other moments of vengeance in the story.