Parris gains his power throughout the play by being in growing support of Danforth as more and more of his parishioners are accused. Parris uses sarcasm and legalistic attention to his religion to help them pinpoint not just sinners, but those who are "with the Devil".
In the short term, he gains a position of respect among the magistrates. Danforth and Hawthorne like to call him in as a witness to his parishioners' abilities to be "Christian". We see this when John Proctor speaks to the court and Parris tries to point out how Proctor has little understanding of the story of Cain and Abel. He further points to Proctor's lackluster church attendance as possible reason for witchcraft.
Parris further finds a short term gain in the court because it gives him moments to grandstand. He makes outrageous claims like:
All innocent and Christian people are happy for the courts in Salem! These people are gloomy for it.
Parris also has the short term gain of getting to pray with so many of the people who went to jail.
As far as consequences go, Parris loses parishioners to death, to jail, and he specifically loses his niece because she fled when she was about to be discovered for the liar that she was. The town's faith and camaraderie is completely destroyed. He loses his ability to preach about anything but hell and damnation. There is talk of a riot in the town and Parris is perhaps the only man that could have done something if it hadn't been for his idea to keep the news of Betty a secret in the beginning of the story. This man was most seriously worried about his own reputation in the short term, but in the long term, he destroyed the entire reputation of a town. To this day, you can go to Salem and visit the witch museum along with the graves of John Proctor and Rebecca Nurse.