The most important day of Helen Keller's life was the day Anne Sullivan came to live with her. Keller uses two metaphors to describe Sullivan's arrival. A metaphor is a comparison that does not use the words "like" or "as." In the first metaphor, which she employs at the end of chapter 3, right before Sullivan's arrival, Keller compares Miss Sullivan's coming to God bringing the Israelites out of slavery in Egypt to Mount Sinai in the Promised Land. In it, Keller states the following:

Thus I came up out of Egypt and stood before Sinai, and a power divine touched my spirit and gave it sight, so that I beheld many wonders.

In the second metaphor, which occurs in chapter 4, Keller likens Miss Sullivan's arrival to the light of salvation that comes to a ship lost in a dense fog when it sees the light of shore:

Have you ever been at sea in a dense fog, when it seemed as if a tangible white darkness shut you in, and the great ship, tense and anxious, groped her way toward the shore with plummet and sounding-line, and you waited with beating heart for something to happen?. ... "Light! give me light!" was the wordless cry of my soul, and the light of love shone on me in that very hour.

Both are dramatic metaphors. They are fitting to describe the cataclysmic change Miss Sullivan brought into Helen's life. Before Miss Sullivan came, Helen was trapped by her blindness and deafness. She was increasingly frustrated, as she grew older, by her inability to communicate. She threw more and more tantrums to the point that her parents sought out specialists, such as Alexander Graham Bell, for help. Through Bell, the Kellers were able to hire Anne Sullivan as a tutor for their daughter. Sullivan's arrival was of life changing importance because Sullivan taught Keller how to communicate.