In the end, Robert Jordan and his band succeed in blowing up the bridge that they were on a mission to destroy. But it's still far from a happy ending, or a satisfying resolution. During the operation, they lost Anselmo (very dear to Robert Jordan, and most readers) and Eladio, in addition to the five anonymous men Pablo murders. Then, as they flee, Robert Jordan himself is wounded while on horseback, losing the use of his left leg. Recognizing that if he went with the others he would be too much of a burden for them to have any hope of escaping, he stays behind. He forces the love of his life to leave him to die alone in one last confrontation with the fascists. The book leaves him lying in wait for an enemy officer on the forest floor.
Yes, the ending seems to bring us back to Hemingway's stereotypical studly male character: the guy faces the cruel truth of the situation, leaves his love, and sacrifices himself to buy his friends some time. To add to that image, in his last thoughts, Robert Jordan turns to his own male ideal – his grandfather – and tries to gather himself to face death and the paralyzing pain of his wound. Nonetheless, in a tellingly human way, he admits that he doesn't prove so good at either as he'd hoped.
From the perspective of plot structure, the ending is nicely orchestrated. The book's first sentence is mirrored in the last, once more describing Robert Jordan lying on the "pine needle floor" and waiting. In many respects the ending ties together other themes from the book. Take the repeated image of Robert Jordan on the forest floor itself – what's its significance? One possibility to consider is that it calls attention to Robert Jordan as an individual at once alone and in relation to the larger world – of nature, yes, but of everything more generally. He feels a certain bond to that world (and not just because, as we learn at one point, pine needles are among his favorite smells). Yet it also remains indifferent to him and the (for Robert) agonizing fact of his death; we see some of that in his last thoughts. Throughout, the book contrasts the connection to nature felt by Robert Jordan and other characters with nature's (and "humankind"'s) lack of concern about their own suffering and death.
This takes us back to Donne's idea of human community in the epigraph, and offers us one last opportunity to evaluate it. Robert Jordan is dying for others, and tells himself at one point "I don't mind this at all now that they are away […] Look how different it would be if they were all scattered out across that hill where the gray horse is [the gray horse is dead]" (43.384).
Yet, when it all comes down to it, he is left alone to face his pain and his own death, and feels at times the full force of that loneliness. We get the impression that at times he is just consciously telling himself things (as in the passage we just saw) to make easier on himself what is in reality very difficult. You might also wonder whether he really believes what he tells Maria to get her to leave him – that they are one, and that he will live on so long as she does – or whether he just tells her that so she doesn't die with him. So when all is said and, um, Donne (hehe), does Hemingway agree with his epigraph? What do you think?
One other big question often raised by critics concerns whether the ending broadcasts a message of futility (that is, pointlessness or uselessness). Robert Jordan's mission succeeded – as the return of Pablo in the book's climax predicted it would. But on the whole the attack by the Republicans has almost certainly failed, because the fascists are prepared to meet them. If the bridge operation was only significant to the extent it was part of the larger attack, does this mean that Anselmo, Eladio, and Robert Jordan have risked their lives and lost them for nothing?
Robert Jordan has throughout the book reconciled himself to his own death and to killing others (directly, or indirectly) by the importance it might have for "the cause." However, in this case, due to factors quite beyond his control, his own action contributes nothing to the cause. The attack as a whole is only a loss for the Republicans. Moreover, Robert Jordan had suspected that the attack itself would probably fail, which is why he'd written a report to the officer leading it.
So was it worth it, after all? And did he make the right decision? On the other hand, would we have approved of him if he'd decided not to blow up the bridge, even though it had been assigned as his duty?