Unfortunately, this question is well beyond the format of Quick
Questions & Answers forum and I cannot consider it as a really correct question. You need to study some literature seriously to understand this matter.
To get an idea, please see:
OOP is not the only possible or an a priory superior programming paradigm
To get some understanding of this matter, you really need to develop some object-oriented projects.
You should also clearly understand, that uses some classes or even
keywords does not make a project object-oriented. You need to use OOP formalities the way it really and essentially uses object-oriented functionality like dynamic dispatch
in a ways vital to your program functionality.
Sorry, but direct answer to the question about importance is impossible in principle, because the term "importance" is too vague and because any limited-size fixed judgment on this complex matter would appear as a pure lie, which I would prefer to avoid.