are of 是什麼？

Question

The questions put forward at the meeting are of vital importance.
為什麼要加入of?
are of
不加入與加入的差別為何？

Answer 1

to be of = to have 有
詞性: 動詞, 後接受詞.
The questions put forward at the meeting are of vital importance.
在會議中所提出的問題具有關鍵的重要性。
put forward: 提出