Major Theme
The major theme of Eldest by Christopher Paolini is that knowledge and understanding are crucial in order to help others . Eragon, who is the main character and dragonrider, spends the majority of his time with the elves and continues to learn new things, like how to read and write, use magic, and how to take care of Saphira, who is his dragon, from Oromis and Glaedr. Eragon uses his new magic and swordfighting skills to help win battles, heal the wounded, and go on missions for the Varden.
Minor Theme
One of the minor themes in Eldest by Christopher Paoini is that family is who loves and takes cares of you and not necessarily those are only blood related to you. In the story, Eragon finds out how even though Morzan is his father, Garrow raised him from a child and taught him how to act and behave. Because of this, Eragon reasons that this makes Garrow more of a father than Morzan ever was. Eragon grew up with Roran, even though technically he isn't his brother, but Eragon treats Roran like a brother. These are some examples of what family means.