Mr. Putnam tells Reverend Parris,
[...] I have taken your part in all contention here, and I would continue; but I cannot if you hold back in this. There are hurtful, vengeful spirits layin' hands on these children.
Parris is very concerned about his "enemies" and the "faction" in his congregation that he believes to be working against him. Putnam is a powerful ally, especially when Parris feels that he has so few, and Putnam says that he can no longer take Parris's part unless Parris sees fit to act against the threat of witches. First, the fact that Putnam seems so convinced may actually sway Parris, and, second, that Putnam will abandon Parris to his perceived enemies might also compel Parris to back the witch hunt.
Further, when Parris begins to panic that his daughter and niece will be accused of taking some part in witchcraft, Putnam tells him,
You are not undone! Let you take hold here. Wait for no one to charge you -- declare it yourself.
In other words, rather than wait to be...
(The entire section contains 3 answers and 605 words.)