Through the carefully chosen title of his sixth novel, the punning references to the bus terminal, the allusions to such works as Wagner's Gotterdammerung (1874), the last drama of The Ring of the Nibelung (1852-1897), Mann's Death in Venice (1912), and Leverkuhn's oratorio Apocalypse, Heller underscores his principal thematic concerns. Closing Time is about the aging process and death of individuals, the passing away of the World War II generation, and, ultimately, the demise of the world.

In Closing Time, Heller bravely confronts through the monologues of Sammy Singer and Lew Rabinowitz what it is to grow old: the fears and realities of cancer and strokes; the losses of sexual vitality, memory, bladder control, hearing; the death of one's spouse; loneliness. He also confronts the inescapability of death. Although John Yossarian is still the affirmer of life, in this novel he completes his recognition of human mortality initiated by the Snowden incident in Catch-22 (1961). Through philosophical discussions with Dr. Dennis Teemer about the naturalness of death, through speculation "That's the only way to live, by preparing to die," and through a nightmarish epiphany in which he sees "the Angel of Death double and the gunner Snowden too" sixty-eight-year-old John Yossarian finally knows without a doubt that his life span is limited.

Not only does Heller open his readers' eyes to the deterioration of the body, but he also provides an elegy to the World War II generation. In fact, the novel opens with Sammy Singer's lament that soon there will be no World War II veterans — only mementos and perhaps memories passed on from parents to their children. The world of buildings without elevators; of George C. Tilyou's Coney Island amusement park rides; of corporate dominance by RCA, Time, and Western Union; of Marilyn Monroe, William Saroyan, and FDR is gone. Even Kilroy has died of cancer of the lungs, bone, prostate, and brain.

The most horrific insight that Heller gives his readers is that with one slip of the finger America's supposedly security-preserving technology might destroy civilization. Can underground bunkers save lives? Can those above ground survive in the event of a nuclear holocaust? Heller does not answer these questions in Closing Time. He only leaves us with an ambivalent message: the dim hope of salvation through affirming love as Yossarian chooses to go above ground to be with his pregnant lover Melissa and the Chaplain escapes from imprisonment to return to his wife in Kenosha, Wisconsin; yet, in opposition, the haunting evocation of the Apocalypse in Revelation through a blood-red moon.