The Question and Answer section for Dracula is a great resource to ask questions, find answers, and discuss the novel.
From the text:
“You are quite right. I did not trust you because I did not know you. But I know you now; and let me say that I should have known you long ago. I know that Lucy told you of me; she told me of you too. May I make the only atonement...
Van Helsing draws a circle around Mina to protect her from Dracula's three wives. He sprinkles broken communion wafers along the circle as a barrier to keep vampires, like the three wives, away. It is called a "Holy Circle".
Van Helsing points out that Lucy might be one of the "Un-Dead" and hence needs to be mutilated to be rid of her.