The general idea is to write a persuasive text trying to convince the Grinch that Christmas needn’t be dismal or not worth celebrating.
I only used the premise of this idea as a finisher for the day. There is, however, an activity packet available on Teachers Pay Teachers (link).
This is what our youngest came up with:
“But Jesus called them to him, saying, “Let the children come to me, and do not hinder them, for to such belongs the kingdom of God. Truly, I say to you, whoever does not receive the kingdom of God like a child shall not enter it.”
(Jesus, Luke 18:16-17, ESV)