The Solid Mandala is a novel about love, family ties, and the destruction such things can cause. The deep bond between the two brothers, Arthur and Waldo, holds them together throughout their lives, but their competition and jealousy force them apart. As each becomes more firmly committed to the idea that he is superior to the other, their codependency also intensifies.

Because the author presents them as fraternal—rather than identical—twins, the boys are more easily able to discern and stress the differences between them. They are depicted as two halves of the same whole: possessing different traits from the other, yet lacking wholeness in who they are individually. Although Arthur seems more socially adept, neither develops lasting emotional relationships with other people that can rival their unhealthy mutual obsession with each other. This extreme arrested development plays into the inevitable conclusion of fratricide.

In his modern version of the Cain and Abel story, Patrick White extends the rivalry between the brothers into old age. The rivalry between them over the same woman, Dulcie, suggests that it owes a debt to another version of the biblical story: John Steinbeck's East of Eden. The characters that are clear opposites in many ways—one is a bookworm, for example, while the other is a jock—often seem to be stereotypes rather than individuals. This extreme opposition, combined with their extreme intimacy, raises the suspicion that they may be alter egos, such as Dr. Jekyll and Mr. Hyde, leaving the reader to wonder how firmly the novel is rooted in realism. In East of Eden, the two brothers discover that their most meaningful relationships are with one another, for better or for worse. Other co-dependent pairs, such as Estragon and Vladimir in Waiting for Godot, are called to mind by these characters and the fact that they are going nowhere together.

The symbolism of the title raises spiritual issues that are played out by the depth of feeling between the brothers and their inability to share those feelings openly. The marbles referenced by the title are unique in being opaque, much like their emotions are to them. Part of Arthur's uniqueness lies in his hobby of collecting the marbles and selectively sharing them with others; his brother not only lacks the ability to share but rejects Arthur's gift because he cannot freely choose it. Waldo has resented his brother for many things, for most of their lives. He resents Arthur’s ability to make connections with people, his creativity and intuition, as well as his general success in comparison to Waldo. Waldo sees Arthur’s different ability in a negative light; Arthur, on the other hand, considers himself Waldo’s “protector.” The brothers simply cannot see eye to eye. They cannot form a true, loving bond with one another. With this in mind, it makes sense that Waldo rejects Arthur’s solid mandala. It is a gesture he does not understand, mostly because he does not understand his brother’s worldview. Their inability to understand true generosity of spirit is symbolized through this frustrating exchange.