In A Wrinkle in Time by Madeleine L'Engle, what does Meg have to do break the spell of the dark thing?

Meg has
learned that she cannot break ITs power
over Charles Wallace by mere brute force. This has a
limited effect on
Charles Wallace, breaking his concentration for only a minute. She remembers

that Mrs. Whatsit gave her the gift of her faults, so she tries to figure out how her
flaws can
help her in this situation. Her impatience has made her persistent,
willing to return to
Camazotz to rescue Charles Wallace, even though her
father is close to giving up. It is the
simple yet complicated act of loving
Charles Wallace that rescues him. Meg realizes that this is
the one thing
that IT cannot understand, the unselfishness of love toward someone else. It
has
tried to spread peace by convincing everyone on Camazotz to be like
everyone else. There is
peace through uniformity. Yet it is not the same.
Similarity is not the same as being
identical. It is through the uniqueness
of love for the flaws in ourselves and our
self-sacrifice for someone else
that can overcome evil.