The main theme of the memoir is that with the right educator and education, a person can overcome multiple handicaps to lead a rich and full life. Throughout the memoir, Keller repeatedly focuses on the importance of education.
Helen Keller became blind and deaf at a young age. As her youthful brain developed, her inability to learn and communicate left her increasingly frustrated and difficult to deal with, prone to daily violent tantrums because she felt alone and misunderstood.
The coming of Miss Sullivan, who taught her how to communicate through manual writing, who showed her deep love and affection, and who excited her love of learning, was a radical, life-changing event for Keller.
Keller uses biblical symbolism to emphasize how important her educator and education were. She likens Miss Sullivan's arrival to the parting of the Red Sea, which led the Israelites from bondage to freedom. She also likens it to God taking the Israelites to the promised land. This symbolism suggests how extremely, and to her mind, miraculously, her life changed due to education.