To me having it set in 1987 feels to modern for this story to be so isolated. There would be news crews and videos plus pictures taken.
Beyond that the moive doesn't establish what powers the demon has or how they are able to fight it. Without a deep knowledge of the catholic church it is hard to understand what's happening.
As a fight between the preisits and a demon neither side has many punch to throw. The priest chant a prayer while the demon trys to get them to lose their faith. For a 1 hour and 45 minuet moive for one side to sit there while the other uses its only punch twice isn't very exciting or intresting.