Death's soliloquies are a motif in the novel. For example, at the start of Part 3: The Struggler, Concluded, Death promises that he will bring Max and Liesel together within "a few pages:"
The juggling comes to an end now, but the struggling does not. I have Liesel Meminger in one hand, Max Vandenburg in the other. Soon, I will clap them together. Just give me a few pages.
Soliloquies appear most often in drama, not fiction. A soliloquy might simply look like a character narrating their thoughts, or it might be a more direct address to the audience outside the earshot of other characters. In either case, soliloquies play on the idea that there is an audience watching events unfold onstage. They are a way to give the audience privileged insight into what is happening—insight that one character has but others do not.
In a novel, most of the characters are incapable of performing soliloquies because they cannot speak directly to the reader in their own voice. The narrator, however, can. A soliloquy in a novel typically draws attention to the narrator and the control they have over the delivery of the story. In this passage, Death pauses the action of the plot in order to speak directly to the reader about his power to "clap [Liesel and Max] together." The soliloquy emphasizes not only Death's power, but also the powerlessness of the characters to drive their own destinies.
Death's soliloquies frequently have something to do with his power and omniscience. However, unlike many narrators, he does not seem to relish in this power. He would rather not know all he does about the way the characters die. He would rather not carry away the souls of children like Rudy, simply because war demands a human toll. As a motif, Death's soliloquies emphasize the ambivalent tragedy of the novel: of course all the characters must eventually die in the grand scheme of the universe, but it can hardly be just for many of them to die in the horrible ways they do. Furthermore, the soliloquies emphasize the futility of many characters' attempts to direct the course of their lives. The choices characters make are intensely meaningful in the novel, and yet they make these choices in a sea of other human choices. Very few people can control the way the tide of human choices will push them.