What is the difference between "of importance" and "important"?

I want to know the difference in meaning between "of importance" and "important" as in " It is of importance to me." and " It is important to me." please, give me the answer..

Instead of "a beautiful woman" you can say a woman of great beauty.

A powerful man can be changed to a man of power. And so on.

In Latin grammars such genitives instead of an adjective were called genitivus qualitatis, genitive of quality. It is a simple rhetoric device. Of course, the genitive has more weight and is more conspicuous than the normal adjective. But such formulas are a means of rhetorical style and hardly used in normal spoken language.

https://books.google.com/ngrams/graph?content=it+is+important%2Cit+is+of+importance&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cit%20is%20important%3B%2Cc0%3B.t1%3B%2Cit%20is%20of%20importance%3B%2Cc0

Although both would be "correct," the version with important is far more common, to the extent that the other version sounds a little funny. You would certainly hear It is a matter of great importance as a set expression, however.