Learning proper grammar is important because it is the language that makes it possible for us to effectively talk about language. Grammar names the words and word groups that make up sentences not only in English but in almost any language. We always associate grammar with errors and correctness.
Grammar is important because it provides information that helps the reader's comprehension. It is the structure that conveys precise meaning from the writer to the audience. Eliminate grammatical errors from your writing, and reward your readers with clear communication. :)
C. Unferth is jealous because the woman he loves want's Beowulf and not him. If you take a look in the book you can very clearly tell that Unferth is jealous of Beowulf and twists the stories to make it sound like Beowulf isn't very heroic and things of that manner.