What is the dramatic significance of the 1st act of Arms and the Man?

The first act is the opening scene of the play. Any
opening scene is supposed to introduce some of the main characters as well as the main
theme(s) of the play. Here in Shaw's Arms and the Man, we are
introduced to the Petkoff household which is the place of dramatic action, and also to
the romantically disposed young Petkoff daughter, Raina, who is going to be one of the
majormost dramatis personae. The Serbian artillery man, Bluntschli, who secretly enters
Raina's bed-chamber through the balcony, is the Shavian spokesman in the play, the
professional soldier as opposed to the "hero of Slivnitza" Sergius Saranoff. We come
across Raina's mother, Catherine, who informs her daughter of the sensational Bulgarian
cavalry charge as led by Raina's betrothed love, Sergius, her description of the
glorious victory of Sergius being soon undercut and terribly mocked at by the fugitive
Serbian mercenary. The scene thus introduces both the theme of war and soldiering and
the theme of romantic-sentimental love as divorced from real life. The scene ends with a
newly-aroused sympathy on the part of Raina for the fugitive having fallen asleep in
Raina's bed.