The speaker uses rhetorical questions to convey his conflicted feelings and uncertainty. In the fourth stanza, the speaker asks four different questions about the rebels. It is not merely that he has questions, but the fact that his questions cannot be answered—and that he continues to ask questions even after he knows they cannot be answered—that conveys how difficult it is to know how to respond to the Rising.
The speaker first asks in line 59, "O when may it suffice?" In other words, when it comes to situations like the rebels', how much "sacrifice" will "suffice" to achieve a goal? He does not find an answer to this question, but he also denies that it can be answered: "That is Heaven's part." Humans can never be completely certain what their efforts will achieve, so the question "What is necessary to achieve our goal?" is not the kind of question they can answer. Nevertheless, the speaker cannot help asking the same kind of question again in line 67: "Was it needless death after all?" That is, was it necessary for the rebels to die to help secure independence?
Asking this question again when the speaker has already judged that it cannot be answered shows how difficult it is for him to arrive at one settled response. He would like to simply put aside his questions and doubts and honor the rebels for their bravery. Still, he cannot help wondering what their bravery achieved and how it might have misled them. Maybe all the brave acts in the world will never be enough to reach the goal. On the other hand, maybe these brave acts weren't even needed to reach this goal. Should he pity them for their fruitless effort? Or should he criticize them for their bad judgment?
Once again, though, the speaker rejects these questions. It is "enough," he declares, to "know they dreamed and are dead." He doesn't need to know what their deaths accomplished to know he should honor them for being willing to die. And yet, he still asks one final question: "And what if excess of love / Bewildered them till they died?" He still wants to know what drove them to their deaths. This question, too, goes unanswered. He moves instead to writing out the rebels' names in tribute. But even as the poem ends by honoring the rebels, its multiple unanswered questions show how difficult it was for the speaker to arrive at this response.
The questions also undercut any straightforward political message that readers might take away from the poem. The speaker honors the rebels, and the rebels used violence to try and achieve their goal. But that doesn't mean that violence itself should always be honored or admired; the speaker emphasizes that there is far too much doubt about the rebels' judgment and effectiveness for that. Suggesting that the rebels should be honored but not necessarily imitated is part of what makes this poem so complex. The rhetorical questions help create that complexity.