To be of?

The "of" expresses the problem's belonging to an important matter:

This problem/question belongs to an important matter.

"To be an important matter" is also ok.

EDIT: I am not sure whether you shouldn't say: "to be of important matter" — without the indefinite article. I feel "matter" works better as uncountable here.

Yeah, what do people mean by "It's of importance" Is it different from the others?

All those phrases mean "it is important".

Why don't people just say" It's important" sole?

Hi,

I have a sentence: it's of an important matter This is not very idiomatic. If you want to say something like this, more idiomatic would be -

I have a sentence: it's about an important matter.

Why don't why say" It's an important matter" but use this structure here?

I have

Belly:

Is your example this:
«I have a sentence: it's of an important matter»

or this:
«It's of an important matter»?

It just seems to me that Clive wrongly took the "I have a sentence" clause as part of your example. You just have this entence...

Didn't you mean:

I have a sentence: "It's of an important matter" (with quotes)

Sorry, perharps my example sentence was wrong. The exact sentence must be:

"It's of importance"

Hi,

Sorry, perhaps my example sentence was wrong. The exact sentence must be:

"It's of importance"

OK, I see you didn't mean what I thought you meant.

Before we answer, can you provide some more context for your example, to show what 'it' refers to. Do you mean, eg

Please look at this letter.