Reading is a Good Way of Learning Polish
What should you read? Really you should read whatever you enjoy. Simply because if it is nothing more than an irksome duty, after a while you will cease to do it. Fortunately due to the Internet it is possible to read Polish newspapers with no trouble at all. Books may also be found this way, though personally I prefer to hold the book in my hand. If you enjoy reading a book in English try reading it in Polish. If you do not understand some of the Polish text you will remember the English, and following a story that you know will make it easier. Not every English book is available in Polish, that Harry Potter is and so is the Lord of the Rings.
Is it necessary to read in the Polish language? In absolute terms, no it is not; but if one wishes to receive a letter and be able to read it or exist as an adult in a Polish community, the ability to read is essential. If one is interested in historical or contemporary Poland then it is highly desirable to be able to read about your interest in the Polish language. There is an enormous amount of Polish written material, which is most unlikely to be translated ever. At a more advanced level, the differences between written Polish and written English give an interesting insight into both national characters.
Poles write on every subject that one can think of, so if one has some sympathy and interest in Poland it makes sense to read Polish. All this so far is directed at printed Polish and does not apply to hand written Polish. Personally I have no difficulty with graffiti on the walls, though having read the message I do understand its significance. I do have difficulty with the small blurred scrawl that seems to be the distinguishing feature of junior officials. It should be remembered that any document is legal in Poland if it is signed and stamped; legibility is not a condition of legal validity.
Obviously if you have a personal reason for learning Polish such as a relationship with a Pole; if you are able to read, then you will understand the name day cards and other expressions of goodwill that you may receive from your partner's family. As in English so in Polish, there is certainly literature, which is associated with the national psyche. Nobody reads all of his or her national literature but almost everybody is familiar with at least some of it. In England Shakespeare springs to mind immediately; in Poland, Sienkiewicz and Mickiewicz. Obviously Poland has many more distinguished writers and poets, but having some knowledge of Sienkiewicz and Mickiewicz is a minimal requirement for understanding literary allusions.
In fact whether one reads in Polish as a second language or reads some other language, one gains another dimension because the material is not written from a British point of view. Not necessarily better but essentially different and therefore well worth reading in Polish.