work hard is of great important to us这句话中为什么有个of?

这本身是个错句子.正确的是：
working hard is of great importance to us.
名词为抽象名词,说明事物的性质时,就用be of +抽象名词之一结构.相当于be+抽象名词所对应的形容词,所以上句还可表示为：
working hard is greatly important to us.