The Lilies of the Field is a story about the power of altruism. A strong, talented African American man and a group of German nuns in the Rockies are characters that form a seemingly unlikely close bond. However, their differing backgrounds—Homer, the protagonist, being Southern Baptist, and the nuns being Catholic—illustrates the fundamental concept of creating a diverse community. Homer feels particularly called to the mission of assisting the nuns. He isn’t sure why he feels called to do so, though both parties seem to gain something meaningful from the church building. Homer works hard to bring money in for both himself and the nuns, even though the nuns will not pay. When the nuns decide to show their gratitude toward Homer by prominently featuring St. Benedict the Moor and a painting of Homer by Sister Albertine, this reiterates the altruism theme of the story: that sainthood or saintliness is achieved through acts of kindness, even if you're just a regular man, like Homer.

Consider, too, Livingston’s racism. Though not the central idea of the story, it is impossible to ignore the role of race. In fact, Livingston’s racist attitude proves to be one of the catalysts in Homer's decision to finish the chapel. Homer wanted to prove Livingston wrong, and he does so by showing his work ethic and talent. Instead of remaining with Livingston for the pay, he returns to the nuns and works out of the goodness in his heart. 

An important theme in the story is the strength of faith—whether religious faith or faith in humanity. This is illustrated by Homer's numerous failed attempts to walk away from the nuns' increasingly involved projects; he always felt an instinct that prevented him from abandoning them. A man of trade, he expects to receive compensation for his work, but he later realizes the values of altruism and goodwill. He puts his faith in the nun’s mission—he doesn’t know why he continues coming back despite the lack of pay. The nuns, in turn, put their faith in him. This is evidenced by their increased reliance on him and their eventual celebration of him through the portrait that hangs in the church. 

The themes of free will and divine intervention are both explored in the story. The nuns believe that Homer was sent by God to assist them in building the chapel. However, Homer, despite being from a Christian denomination himself, believes that it was he who decided to help them, not God. The story can be interpreted in two ways. If he was sent by God, then the story is about the power of faith and divine intervention. If Homer simply decided to stay and help, then the moral of the story is that "godliness" exists within all humans in the form of altruism, and God is not needed to intervene. Or, perhaps on a broader scale, there is evidence of the goodness of humanity everywhere. Perhaps when people are called to certain endeavors, they are being called to express their humanity.