Staying at reading a book

Hi Jerry,
I was able to get my hands on the Left Behind series, and I'm 3/4 of the way through the first book. I've enjoyed the book so far however, for me for some reason it is difficult to stick with a book and finish it all the way through no matter the book I read. Do you have any suggestions as far as finishing a book to the end or is it just something that I have to force myself to keep at it until it's finished.