Kate being the one to deliver Claire's baby is full of subtext and foreshadowing. Kate eventually raises Claire's bab when they get off the island.
The same of Claire's delivery is also the moment that one of the candidates witness again as they travel around in time. I am ashamed to say I don't remember which one but I think it may be Jin.
Jack angrily tells Sun, "Don't tell me what I can't do." This echoes Locke's mantra. It's not unusual to see Jack and Locke exhibiting the same degree of stubbornness, but it's usually not so on the nose.
Jack's wedding to Sarah it's one of the very few times his father actually gave him decent advice.
Little Aaron was born about the same moment that Boone died. There were no references later on in the series about any connection between the two, but it would have been interesting. If Shannon hadn't died, they might've thought about it.
Jack learns about letting go in this episode, but I'm not sure if either he didn't learn it well enough or needed this experience to fully let go at the end of the series. I think it's the latter.