Happy: feel or show pleasure, satisfaction, satisfaction, etc. (feel or show pleasure, satisfaction, satisfaction, etc.); Happiness; Happy)
For example: happy marriage, scenes, memories, children, ending (for a book, etc.), happy scenes, happy memories, happy children, happy ending (for a book, etc.).
(in greeting) full of joy (wish) Happy birthday! Best wishes for a happy birthday! Merry Christmas! Merry Christmas to you!
Merry: happy and cheerful; Full of joy and joy (happiness; Pleasant; High spirits)
For example: happy laughter, party, group happy laughter, party, group
Merry Christmas to sb. Merry Christmas to sb.
Happy: enjoying or showing joy, happiness, or good luck, or characterized by it
Mainly refers to physical happiness.
Happy: Full of or showing extreme happiness
Mainly refers to spiritual happiness.
Because Christmas is to celebrate Jesus' birthday, it must be "Merry Christmas" for spiritual happiness. "Happy New Year" or "Happy Birthday" is for physical happiness.
I hope you can appreciate the subtleties from the above explanations in Chinese and English.