There are two sentences there. In the first one, should either say "books" or "a book." Don't use singular countable nouns without an article or some other determiner.
You also make the same error in the second sentence. And you should change "chance" to "chances" and "growth" to "grow." You also need a verb in the first clause of the second sentence. Additionally, you should either change the punctuation or divide it into two shorter sentences.
I would suggest:
To be honest, I never read books for entertainment. I always read books that are related to my major. I think the more I read books related to my major, the more chances I have to learn about my profession.