Final answer:
Helen Keller considered March 3, 1887, as the most important day of her life, marking Anne Mansfield Sullivan's first day as her teacher, not Sarah Kemble Knight.
Step-by-step explanation:
The quote in question actually references an important day in the life of Helen Keller, not Sarah Kemble Knight.
The most important day in Helen Keller's life, as described in the quote, is when her teacher Anne Mansfield Sullivan began to work with her.
The date was March 3, 1887, which Keller recalls vividly as a turning point in her life, marking a significant contrast between her life before and after Sullivan's arrival.
This day is of paramount importance because it signifies the commencement of Helen Keller's formal education despite her disabilities.
Anne Mansfield Sullivan's innovative teaching methods eventually led Keller to become one of the most celebrated educators and activists of her time, inspiring millions around the world.
Commemorating this event holds historical significance as it illuminates the potential for education to transform lives, particularly for those overcoming challenges such as disabilities.