What is the difference between these two sentences?
It's the most idyllic scenes.
It's the most idyllic of scenes.
Thank you very much~
How about if I remove "It's" in these two sentences:
The most idyllic scene.
The most idyllic of scenes.
Is there any difference in meaning?
If you remove "It's" you don't have a sentence. "It" is the subject of the sentence and, as I'm sure you know, a subject is essential to a sentence. As for difference in meaning, see freezeframe's response. There is no other difference.
It is also possible to say: It's a most idyllic scene.
most means (roughly) extremely here.