There is an overall theme of the search for, or lack of, purpose in The Dumb Waiter. Ben and Gus are discussing the purpose behind what they're doing while they await their target. Gus, the newcomer, is a bit confused about how they're performing the hit and why. He wants to understand the purpose of the hit, but that purpose remains unclear in the end. Gus represents all naive human beings who wish to understand the reason for their existence but can't get a clear answer. They go through the motions but debate the way those motions are supposed to be carried out, as shown when Gus questions the semantics of the hitmen's jargon because he doesn't understand it properly.

The action of the play revolves around the idea of deciphering ambiguous messages from beyond. Gus and Ben are receiving cryptic messages through the dumbwaiter requesting the delivery of various foods, although the men are not in a kitchen but a basement room. They are perplexed by these messages but continue responding. They attempt to send up food, hoping to appease the mysterious message-sender above to no avail. Thus Gus and Ben represent the human attempt to decipher messages from God or the universe about their purpose and doing what they can to appease this higher power they cannot understand.

Gus and Ben discuss at length the man they are planning to kill, who is facing his own mortality. It later turns out that Gus himself is the target. This illustrates the idea that people are all too willing to discuss death when it is an impersonal, abstract concept, but when death becomes present and real, it is much more frightening.