Jack is again struggling with his hero complex, and is faced with a dilemma. He can't not fix someone. I'm still wondering what is causing this and if we'll ever find out. Whatever is causing it, Jack is super committed to fixing people at whatever personal cost to himself, and this episode forces him to realize that he can't save everyone. Claire is having her baby at the same time that Boone is hurt. Both are in desperate need of a doctor's care, but he has to choose who he will help. He chooses to help out Boone, and probably rightly so, but it's still not an easy decision for him, or even the others to handle. Claire isn't too happy that Jack isn't coming!
His flashbacks also show us that not only is Jack committed to fixing people, but so much so that he can't let go of people when maybe he should. We see that he's struggling with why he's marrying his wife, and if it's because he was able to fix her and he can't give up on her. Whether or not this is true, it's telling that he's wondering if it's the case since he seems to at least recognize he can't let go. He also can't let go of Boone when it's hopeless trying to save him. Boone has to tell him it's ok to let him go, that he's fine with dying and realizes he can't be fixed. How sad it is that the dying man has to tell the doctor it's over! But even then, it takes Jack some convincing before he'll give up hope.
We are left at the end of the episode with the now familiar opposites of the island. One man dies, another is born. Whether Boone and the baby will be connected in anyway have yet to be seen, but once again the island gives and takes in it's fashion of black and white, death and birth: polar opposites.