If you watch Parris in the opening scene, his biggest concern is his reputation. He is less concerned with Betty's condition than he is about what his parishoners are going to think. This effort to hide put a series of events into play that took a dangerously deadly turn. Had Parris been more concerned about Betty's well-being and promised no retribution to Abigail, she likely would not have begun the set of lies that began that first scene.
Later, Parris is concerned with his salary (once again, a selfish purpose). In seeking an answer or an end to this means, he finds himself at odds with church attender John Proctor. To further the plot, John's attendance or lack thereof is brought to light by Parris and a personal bout between the two of them begins. Parris allows himself to be played by Thomas Putnam who also has angst for Proctor.
As the play nears the end of the third act, Parris is supporting all accusations of witchcraft that the girls make and seems to be out for revenge although he likely names it justice or spiritual morality.
By the end, Parris begins to understand that way too many people are being condemned and that they are good people. Unfortunately by that point, it is too late. This demonstrates his understanding of the perpetuation of the Trials.