In his short story, Saki highlights two different philosophies of life that are antithetical to each other.
Reginald, the male protagonist, values a simple, unencumbered life of freedom and autonomy. He has a wonderful sense of humor and expects to decide his own destiny apart from any religious authority or system. In that sense, he acts as a foil to Amabel, a beautiful and intellectually gifted vicar's daughter. Amabel favors a different philosophy of life, one that allows her to live her life according to a specified creed of absolute values. She favors a didactic or pedagogical perspective, one that aims to imbue every human action on earth with some sort of moral significance.
...she never played tennis, and was reputed to have read Maeterlinck's Life of the Bee. If you abstain from tennis and read Maeterlinck in a small country village, you are of necessity intellectual. Also she had been twice to Fecamp to pick up a good French accent from the Americans staying there; consequently she had a knowledge of the world which might be considered useful in dealings with a worldling.
Filled with religious fervor, Amabel tries to convert the wayward Reginald but is unsuccessful. Reginald, for his part, manages to out-maneuver the self-righteous vicar's daughter by hijacking the choir's outing and investing it with a faintly Bacchanalian air. First, Reginald lulls Amabel into smug complacence by using religious language to describe his enthusiasm for her project.
Reginald called it a dispensation; it had been the dream of his life to stage-manage a choir outing.
The children are then given tin-whistles to imitate the pipes they should have had, and Reginald appropriates a he-goat to lead the proceedings through the village. Some of the children are wearing their spotted handkerchiefs on their persons, and the whole choir is singing a temperance hymn of sorts. The story ends with the proclamation that 'Reginald's family never forgave him' for his exploits. There is no mention of Amabel's reaction; the author's silence on this matter is telling. Perhaps, we are to assume that neither Reginald's family nor Amabel has a sense of humor.
In the story, Saki illustrates how different Reginald and Amabel's philosophies are. Reginald maintains that 'beauty is only skin deep.' Here, he may be speaking about more than physical beauty; he may also be intimating that actions alone cannot accurately testify to the purity of one's motives. By extension, adherence to strict religious ritual is not a testament to one's moral virtue.
Saki's "Reginald's Choir Treat" illustrates two very different philosophies of life. First, readers are introduced to a life which is conservative and religious. This philosophy is illustrated by through the character of Amabel. Amabel is intellectual (noted by her not playing tennis), preached repentance, and embraced the concept of living a full (sin free life). Reginald, on the other hand, follows a more daring approach to life. He believes in questioning everything (with cynicism) and being daring. He questions everything Amabel brings up, especially about internal and external beauty.
Reginald constantly chastises Christian life, most prominently illustrated by the narrator's first comment on him: "Reginald was a pioneer." Essentially, as a pioneer, Reginald challenged everything.