In Act IV we see a worried, distraught Reverend Parris. In the preious act was a firm supporter of the trials and willing to charge anyone who didn't support them as being against the trials, him, and even God.
However, as Act IV begins, Parris has changed (just like the town). He comes to the court visibly shaken and upset and reports to Danforth that his niece Abigail and Mercy Lewis have run away. What makes this worse (he is clearly not worried about the girls' well being) is that the girls have broken into his safe and taken his savings.
Thirty-one pound is gone. I am penniless. He covers his face and sobs.
From Act I we have witnessed Parris' concern over his career, his ministry, and his status in town. He went against his intial beliefs that the girls were afflicted with witchcraft when he saw it could actually benefit him if there was such afflictions. Now, his biggest fear has come true. He has lost everything.
Parris also realizes that if Abigail and Mercy Lewis have run away because "they fear to keep in Salem any more" it will only be a short amount of time before others in the town also turn against the courts.