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The gift that Mrs. Whatsit gives Meg is her love. She tells Meg that she loves her and that boosts Meg’ spirits a lot. Knowing that someone as wonderful and powerful as Mrs. Whatsit has love for her makes her feel very special. Mrs. Which’s gift to Meg is the one thing she has and IT doesn't. Meg struggles to find out what this means but as she is fighting IT, she realizes that the one thing that she has and IT doesn't is love; IT is entirely incapable of love. Meg’s love for Charles Wallce ends up weakening IT, setting Charles free, and bringing them all back home.
A Wrinkle in Time