What is the central conflict of Shoeless Joe?

The popular film Field of Dreams was based on W.P. Kinsella's 1982 novel Shoeless Joe.

In the book, Ray Kinsella experiences "magic" in his field, hearing a voice advising that "if you build it, they will come." Although he is financial difficulty, Ray commits to building a baseball field on his land. He is opposed by his brother-in-law, Mark, who wants to buy the land and build apartments there. One central conflict is between Ray's idealism and optimism and Mark's pragmatism and pessimism.

My relatives... know I am a baseball freak and dispair that I have corrupted their daughter... they all hope Mark will be successful in buying the farm. Then I will be forced to go back to selling life insurance, and perhaps Annie will come to her senses and leave me.
(Kinsella, Shoeless Joe, Google Books)

Although both his extended family and friends all try to convince him to abandon his dream, Ray continues to build, eventually enlisting author J.D. Salinger to help. At the end of the book, Ray is able to make the baseball field a prosperous tourist attraction, realizing his dream and reconnecting with the memory of his father.