Final answer:
The Grinch learned that the spirit of Christmas is about community and giving, not material possessions.
Step-by-step explanation:
The lesson the Grinch learned on Christmas Day when he realized Christmas came is about the true essence of the holiday. He discovered that Christmas does not depend on the material aspects such as gifts and decorations, but rather on the spirit of community and the joy of giving. Despite his efforts to steal Christmas from the Whos by taking away their presents and feasts, Christmas still arrived, teaching him that the celebration is about more than just physical possessions.