The generational motif
The story follows three generations of good men falling at the hands of evil people, but winning in the end through their legacy or fate. This constitutes a generational motif, because it's grandfather, father, and then son, and their actions are in accord. This shows family honor as one way of overcoming death.
The good king and bad king
Another basic dilemma of the book is the problem of good and evil, depicted most basically as good kings and bad kings. Volsung's reward for a life well-lived is the blessing of his son, but that doesn't spare him from death. But Atli, the bad king, earns himself a dishonorable death when he's passed out drunk after an orgy. His house burns down on top of him.
The allegory of love and death
One of the tragedies of the Sigurd story is that he never gets to live with his lovely divine princess, Brynhild. Instead their pitted against each other by forces out of their control, and yet ultimately, they are together in death because they share a funeral pyre. Thus their love has overcome their own deaths.
The symbolic poisoning
Sigurd's character is not corrupted, his mind is, because he is tricked into administering a potion to himself which changes his passions. This is a kind of possession by a chemical, so it has symbolic connections to real life addictions. Perhaps the potion represents the mistakes people often make when they are drunk. That would make sense of the final image of justice for Sigurd in the death of the drunkard king Atli.
The divine princess
Odin gets grumpy with his kids and often sends them to earth to learn their lessons within the confines of human life, which in Nordic thought constitutes something like divine justice or divine law. Odin's judgment is often binary, because it does something good and something bad. The princess's brutal punishment is human life and death, and the disappointment of futility on the earth. But she also gets to fall in love.
