Proctor insists that Mary warren testifies in Elizabeth's defense because his actions lead Elizabeth to the trouble.
Mary Warren refuses to testify because she is scared of Abigail
Explanation:
First of all, Proctor insists that Mary Warren should testify because that way is going to be able to help Elizabeth after he committed many mistakes. After realizing that his innocence if proven might create trouble for his family. So he wants to prevent that.
For the second question, Mary refuses to do it because she knows what Abigail is capable of after signaling many people for witchcraft and gaining influence by it and her position as the niece of Parri's.
