Question

is of great importance这是什么语法点

Answer 1

1、“be of+抽象名词”，这时的of短语相当于这个名词的同根形容词，作为表语表示主语的性质或特征。of的意思是“具有、具备”等.
of importance=important

2、“be of+集合名词或其它类型的名词”，相当于belong to或have。of表示归属关系或“有”的意思。
The army and the people are of one family.=The army and the people belong to one family.

3、“be of+物质名词”表示主语是“用某种材料构成或制作的”，相当于be made of或be built of。
Our building was of bricks.=Our building was built of bricks.

Answer 2

be of+名词结构中的名词是抽象名词时,相当于其中名词所对应的形容词的意思，说明被修饰词具有某种特征或属性。常用的名词有 use/importance/help/value/interest/quality/service/benefit/necessity等。例如:
1、is of great importance 就等于is greatly important意思是非常重要 。
2、It is of no interest to me就等于 It is not interesting to me 我对此不感兴趣。