Severus Snape's Patronus was a doe because it symbolized his deep and lifelong love for Lily Potter, Harry's mother. Snape's Patronus taking the form of a doe, which was also Lily's Patronus, reflects his unwavering devotion to her despite the love being unrequited. This form of Patronus reveals the tender and hidden side of Snape, contrasting with his otherwise harsh persona, and signifies his true loyalty and the emotional core behind his actions throughout the Harry Potter series. His Patronus served as a magical manifestation of his happiest memories and the love he carried for Lily from childhood.

Why the Doe?

• The doe is a gentle and nurturing creature, symbolizing grace and determination, reflecting Snape's secret love and good intentions.
• Patronuses are typically tied to a witch or wizard's emotions and can change with strong feelings; Snape's Patronus changing to a doe shows acceptance of Lily's choices and his commitment to protecting her son, Harry.
• The doe complements the stag Patronus of James Potter, Lily's true love, highlighting the tragic love triangle background of Snape's character.

This meaning was emotionally powerful in the narrative, revealing that Snape's true loyalty was not to Voldemort but to Lily and, by extension, Harry, who he protected because of his love for her.

In summary, the doe Patronus is a magical symbol of Snape's enduring love for Lily, embodying both his past and his motivations within the story.