When Ray hears the mysterious voice's prophecy, he realizes that he has to literally build a baseball field in order to fulfill that prophecy. In Biblical and other religious texts—or even in folklore and mythologies—prophecies are metaphorical in nature. They are riddles that, on the surface, seem to be literal but are actually metaphors that would lead to a grand existential or cosmic lesson. In that regard, there is one Biblical character who is similar to Ray: Noah. When God warned Noah of a global flood that would literally and figuratively cleanse the Earth, Noah was instructed to build an actual ark. Likewise, Ray was to build the baseball field in order to complete the voice's prophetic vision.
Ray, who is an avid fan of baseball, also realizes his dream of becoming part of he game and not just limited to being a fan or observer. When he is given another instruction by the mysterious voice, to "ease his pain," he kidnaps reclusive author J.D. Salinger in order to take him to a Red Sox game. This level of dedication to the voice is similar to the supernatural voice that inspired many religious prophets throughout history.
When Ray, Salinger, and the hapless former-player, Archibald Graham, return to Ray's baseball field, they all attain their respective dreams, especially Graham and Ray. In this sense, Ray not only fulfilled his dream of meeting Joe Jackson and being a part of the game, but he also fulfilled Graham's dream of redeeming his short-lived professional baseball career.
The sub-conflict in the story pertains to Ray's turbulent relationship with his late father. The baseball field—which is evidently a portal to the afterlife or another dimension—made it possible for Ray to make amends with his father's spirit. His father was the one who introduced Ray to baseball and instilled in him the love for the game.
In essence, the baseball field was a supernatural phenomenon that was meant to tie loose ends and offer redemption for those with a tragic past. Had Ray not listened to the mysterious voice and built the baseball field, none of the characters' respective dreams would have been fulfilled.