The novel's epigraphs deal with the season of summer—its joy, ripeness and provision of pleasurable opportunity. Greeley often represents pleasure in food forms. As a small child, Jane befriends Leo by purchasing him a Good Humor Bar. As an adolescent, she works in a soda fountain in the summer. Whenever Leo sees her during his youth, she is associated with delectable treats.

By contrast, the plot deals with opportunities lost, withdrawn, unseen, untaken, or misperceived. Going over it, either in mental review or with a pen in hand, is the only way to make sense of it. Greeley fills the novel with allusions to Marcel Proust's Remembrance of Things Past (1913- 1927; see separate entry) to underscore this theme.

There is another set of allusions to F. Scott Fitzgerald's The Great Gatsby (1925; see separate entry). Leo Kelly at first unconsciously, then with deliberate consciousness, compares himself to Gatsby's Nick—an outsider and distant observer of the nouveau rich and their careless pursuits. When Jane's brothers endow a Chair of Irish Studies at the university, Kelly wryly accepts it less as a gift than as proof for the thesis of his scholarly book. Bad money may follow good money, but modern universities welcome it nonetheless.

In unpublished correspondence, Andrew Greeley wrote: "Summer at the Lake is about second chances—and whether you get a third chance if you blow the second. Does God give us AT chances? Or should I say C chances?" The themes of water as renewal /baptism and summer as a time of pleasurable indulgence are combined with a theme that permeates the whole of Greeley's writing—that men and women are signs/sacraments to each other of God's enduring love. Sensual indulgences such as skinny-dipping or eating double-chocolate ice cream bars may not be the common symbol systems theologians use to represent the presence of God's love, but they are Greeley's shorthand. The novel ends with an allusion to James Joyce as Jane echoes Molly Bloom's sensual, "Yes," she said, "yes."

Another common theme of Greeley's novels is that the Church is not its hierarchy, but its people. Fr. Keenan finds support in the Catholicism of the Keenan family, if not always in the workings of the Church itself.