Steinbeck created this sense of a cycle because that is what life is for us. Every book has a purpose to comment on real life issues that we might not only enjoy the text but be challenged to think about how this issues play out in our own lives.
Obviously a sharp theme in this book is sacrifice. George has sacrificed much of his potential for pleasure so that he can take care of Lennie. By this point in the story, he makes the ultimate sacrifice by giving Lennie a pain-free death and positioning himself to be caught by Curley as if he was doing Lennie a favor so Curley could not torture him.
The imagery of the location reflects complete and total serenity and perfection, something we hope for in an after-life. Hopefully George just sent Lennie there.