"The Unknown Citizen" is a sinister elegy delivered by the government for a man who has recently died. There is tension between the contents of the elegy and the description of the man as "unknown." In fact, this isn't an unidentified man, but rather one whom the government seems to know everything about. The poem even begins with an inscription that looks to be some sort of identification number! The poem, then, asks the reader to think about other ways in which the man could be described as "unknown."
The poem opens by offering a general report about the man's life. Most of the poem follows a similar formula—a specific institution offering its creepy approval of the man for behaving in the "correct" way. This praise is, of course, steeped in irony—Auden's poem criticizes over-bearing state control and invasive surveillance (and, perhaps, the man's own willingness to conform). So it is the "Bureau of Statistics" that offers the dead man the high praise that "there was no official complaint" against him. In other words, he never did anything to upset the system. There was no particular praise of him either; he was considered good just because he never did anything wrong (at least anything that the state knew about).
The fact that this ultimate judgement is issued by this particular institution speaks to a particular ideology about human life and society—that it can be measured, understood, and even improved by scientific statistical analysis (implying that there is no part of being human that can't be quantified).
Lines 3 and 4 then state that numerous "reports" on the man's "conduct" are in agreement that he "was a saint" and was a faithful servant of "the Greater Community." Here Auden builds a wider picture of this dystopia of surveillance and suspicion. The dead man is a "saint" not in the religious sense but in his obedience to the state, placing the state in a powerful role akin to that of God in earlier centuries.
In this section, the state—which, it's worth remembering, is also the speaker here—co-opts the language of humanity for its own purposes. So the notion of "community" is no longer about genuine togetherness and empathy, but relates more to an individual playing their role in fulfilling the state's vision for society—one in which everything is controlled and micro-managed through bureaucracy and official authority. The capitalization of "Greater Community" makes into just another state institution—like the "Bureau of Statistics"—rather than something that develops organically within a society.
The caesurae in line 4 (those pauses after "That" and "word") help the poem mimic the rhythms of speech in a real elegy, showing another way in which the State imposes itself on the language. Also notice how the rhythms and language in this section—and elsewhere in the poem—evoke the rhythms of an official report—it's easy to imagine this speech being written in a government office!