"是……的" is a common structure in modern Chinese.
It's primarily used to highlight your point or make an emphasis. Pretty much like the "It is …… that" or "Someone does do something" structures in English.
这本书是她买的。
It is she who bought this book.
我是三年前学的游泳。
It was three years ago when I learned swimming.
我是有看法的。
I do have some thoughts (on this issue).