The last thing Sophie left for David to remind him of her. It symbolises their friendship and how far they have come along, as earlier reference to chapter 1 there was a scene about her hair and ribbons flying smt like that
This shows David's weakness, something he rarely shows to Mr Wender as they had agreed that they were on a man by man basis, so this show of vulnerability showed how distraught he was right now
It shows how close Uncle Axel is to David, such that he ensures that David doesn't repeat the same mistake he does to ensure his safety. In the chrysalids, Uncle Axel is seen as not as tightly rigid as the other Waknukians, having other views and this later further bonds David, who we discover is a telepath
It shows how much Sophie mattered to David at this point in time, given that he was so concerned about her fate after a dream. The thought of wanting John and Mary Wender to know of his thoughts also goes to show how their opinions on him now strongly mattered to him, and how he wants to reassure them about their worries
He doesn't give leniency for even family but rather is even harsher and stricter on them
Shows Joseph's intolerance to deviations, even if it was only through words
became a person like a teacher to David which tells us how highly David regarded him and his opinions, though he can still feel Mr Wender's wariness
Development of relations [not that impt tho]