This very revealing quote appears in Act 4 of the play, and of course, this is when the madness that has swept through Salem is beginning to break up - Parris relates to Danforth how Abigail has ran off with all the money in Parris's safe and it is clear that there is great public discontent with what is happening. Parris relates how only thirty people came to chapel to witness the excommunication of John Proctor, and then, in the face of Danforth's insistence that there will be no postponement in the hangings, he reveals an incident that has caused him to fear for his life:
Tonight, when I open my door to leave my house - a dagger clattered to the ground. Silence. Danforth absorbs this. Now Parris cried out: You cannot hang this sort. There is danger for me. I dare not step outside at night!
On the morn of the hanging of Rebecca Nurse and John Proctor, Parris is beginning to see that this might have all been a created hysteria which they have been taken in by. And what is more, Parris is now afraid for his own life because of his participation in the Salem Witch Trials. Thus his statement reflects his own doubts about what the girls have claimed and his belief in the goodness of characters such as Rebecca Nurse and John Proctor.
Parris is afraid of the consequences that would follow if the court hangs John Proctor and Rebecca. The two individuals are influential and not known to be of any harm to the society. Rebecca is known as a virtuous woman with a deep disposition to righteousness, while John is deeply disposed toward justice. The people would not take the actions of the court lightly and would likely rebel and retaliate, putting all involved at risk.
Parris: Judge Hathorne -- it were another sort that hanged till now. Rebecca Nurse is no Bridget that lived three year with Bishop before she married him. John Proctor is not Isaac Ward that drank his family to ruin. To Danforth: I would to God it were not so, Excellency, but these people have great weight jet in the town. Let Rebecca stand upon the gibbet and send up some righteous prayer, and I fear she’ll wake a vengeance on you.
Parris tells Danforth of threats to his life after he heard a dagger clatter to the ground as he opened his door. He is aware that the people are unhappy because the trials are a sham and many innocent people have been hanged. He is opposed to the continued hangings because they present a threat to his life.