The play has themes of nationalism and blood sacrifice. Colm Tóibín describes Michael as an "idealistic, inspirational" male hero in the tradition of Lady Gregory's plays The Rising of the Moon and Gaol Gate, and the Irish mythological hero Cuchulainn, because he is willing to sacrifice his life for his newfound nationalistic beliefs, unaffected by the "land-hunger" which occupies his family. Susan Cannon Harris contrasts the play's depiction of the "male patriot" who makes a blood sacrifice which "symbolically regenerates" Ireland, with the female peasant characters who face the arduous tasks of economic reality which make this regeneration possible. Michael abandons the everyday concerns of dowries, wedding clothes and land purchases in order to follow Cathleen and give up his life for the nationalist cause.
Cannon Harris describes the significance of Maud Gonne's performance as Cathleen Ni Houlihan in expressing the play's nationalist themes. Gonne's reputation as a nationalist campaigner and public speaker added to the play's popular appeal. Her disguise as an elderly woman illustrates that the Poor Old Woman is only a veneer who conceals the "uncorrupted essence" of Irish freedom.
Nicholas Grene examines the trope of "strangers in the house" which is used in different contexts throughout the play. The British invaders stole Cathleen Ni Houlihan's land and exiled her, forcing her to wander the roads in search of help. The French invaders are seen as "necessary catalysts" for the banishment of the British colonisers, while Cathleen herself is a disrupting presence when she visits the Gillane family's home and presents them with a past vision of Irish independence which could be achieved in future.