How to use " is of " in sentence

The phrase is not "is of" but
of + noun that is a quality

e.g.
a vase of great value
a man of integrity
a secret of great importance
a project of high returns
a man of great confidence

You can put "It is" or "He is" in front of these sentences and they become
It is a vase of great value
He is a man of integrity
It is a secret of great importance
It is a project of high returns
He is a man of great confidence

The sentences can be written as
The vase is of great value.
The secret is of great importance.

"is of importance" can be explained as "has/have the quality of being important"

You can say
In employment terms, this inhibition has the quality of having little consequence(effect).
Mathematics has the quality of being very useful to many sciences.

is of (a quality) = has that quality
but of course it is very odd to use "has the quality of "

2007-11-15 07:48:18 補充：
I cannot totally agree with louiswaiwong, the poster below.is of is neither fancy nor formal. In fact, it is used quite commonly in daily English.

2007-11-15 07:49:02 補充：
In English, the same idea can be expressed in different ways, and each may differ slightly or significantly in the tone of the speaker/writer, stressing the importance of the idea, or drawing attention from the audience/readers.