The title, Arms and the Man, is an ironic reference to Virgil's Aeneid, which glorifies the warrior. Shaw's play, in contrast, satirizes the idea of the warrior hero, showing Sergius as an incompetent who has blundered into heroism by mistake, and, also reveals that Sergius, despite his highly romanticized wooing of Raina, is, in actuality, seducing her servant Louka.
Therefore, the real "man" in the play is not the supposed warrior hero Sergius, but the pragmatic Bluntschli who deserts the battlefield and show up at Raina's balcony. Bluntshcli does not fall for false romanticism, be it in love or war, and it is he who wins Raina in the end. In the last line of the play, Sergius says of Bluntshli, "What a man! What a man!" Sergius still doesn't understand Bluntschli, but the repetition of "man" in the last lines emphasizes that Bluntshcli is the real man in the play.
"Arms" means weapons of warfare, but it is also a play on the kind of possessive love embodied in the idea of folding a beloved in one's arms as a conquest. Sergius, in particular, tends to gather Louka in his arms as an object he owns. When she questions whether his statement that she "belongs" to him is an "insult," he responds: "It means that you love me, and that I have had you here in my arms." Shaw critiques this idea of love as ownership.