Abigail Williams is very skillful at manipulating people to get what she wants. In Act I, although John Proctor has put an end to their brief affair, Abigail knows that he still has feelings for her. And she plays on this, using a form of emotional blackmail to rekindle their relationship:
I look for John Proctor that took me from my sleep and put knowledge in my heart! I never knew what pretense Salem was, I never knew the lying lessons I was taught by all these Christian women and their covenanted men! And now you bid me tear the light out of my eyes? I will not, I cannot! You loved me, John Proctor, and whatever sin it is, you love me yet!
We also see from this quotation that Abigail plays very much the leading role in her affair with John Proctor. Her roles of leader and arch-manipulator go together.
I am but God's finger, John. If he would condemn Elizabeth, she will be condemned.
Emotional blackmail having failed, Abigail sets out to destroy John's wife, Elizabeth. Only she hides behind God in carrying out her wicked revenge. Doing this makes it harder to challenge her. After all, if she's the instrument of God as she says she is, then how it is possible to contradict her? It's no longer enough for Abigail to play on people's emotions; she must now also manipulate their fervent belief in God to get her own way.