We start with the source of the title: the opening line of Virgil's Aeneid, the story of the founding of Rome. Virgil is announcing he intends to deal not only with the Trojan War but with the man, Aeneus. Shaw, in taking this title, is stressing the differences between Bluntschi, the soldier and… the “chocolate soldier,” that is the peaceful human being underneath the military exterior. Bluntschli, as the underplot of the play reveals, is not really of militant disposition, but much more a lover and humanist. Shaw, here and in many of his other works (cf. for example, Major Barbara, and Man and Superman) finds dramatic fodder in exposing the contrasts between the outer social pretences and the human character disguised by social custom.
The play (1894, early in his canon of some 60 plays) is, of course, a criticism of English society (regardless of its setting in a non-realistic Serbo-Bulgarian conflict) and a comedy meant to amuse all cross-sections of a highly layered English society (the servant class in the play is well developed), but its lasting value as literature can be attributed to Shaw’s insights into the difference between outside actions (which can appear superficially to be brave or heroic) and inner qualities and worth. The battle charge of Sergius (which appears to be bravery but was in fact accidental foolishness) is a perfect vignette of the theme. That he is engaged to Raina but flirts with Louka (his social inferior) reveals to the audience his true character. Bluntschi, on the other hand, appears coward-like by hiding in Raina's bedroom, but is in fact a man worthy of Raina’s love. So the primary theme of the play, resting on the comic business, is the importance of not judging people by exteriors or by social rank, and of looking both at the "arms" and the "man."