That dance is mainly played out between Dr. John "Jack" Seward and his former professor Abraham Van Helsing. Seward, as a psychiatrist, is a modern man of science. But when he is stumped by Lucy Westenra's symptoms, he calls upon Van Helsing, his former professor. Van Helsing soon begins to suspect that something occult is going on, but he refrains from disclosing his thoughts to Seward. Knowing him to be a modern, scientific man, Van Helsing knows Seward will be skeptical about Van Helsing's diagnosis of the problem. Consequently, as things unfold it's between Van Helsing and Seward where the issues of faith and doubt in the modern world come out in the novel.
For example, early on, in discussing Seward's perplexity at Lucy's aliment, Van Helsing says to him:
"You are a clever man, friend John. You reason well, and your wit is bold, but you are too prejudiced. You do not let your eyes see nor your ears hear, and that which is outside your daily life is not of account to you. Do you not think that there are things which you cannot understand, and yet which are, that some people see things that others cannot? But there are things old and new which must not be contemplated by men's eyes, because they know, or think they know, some things which other men have told them. Ah, it is the fault of our science that it wants to explain all, and if it explain not, then it says there is nothing to explain."
Such a great line: "It is the fault of our science that it wants to explain all, and if it explain not, then it says there is nothing to explain."
Later in this same conversation, Val Helsing asks Seward to open his mind, to set aside his scientific prejudices, so that Val Helsing can disclose what he thinks is happening:
"Well, I shall tell you. My thesis is this, I want you to believe."
"To believe what?"
"To believe in things that you cannot. Let me illustrate. I heard once of an American who so defined faith, 'that faculty which enables us to believe things which we know to be untrue.' For one, I follow that man. He meant that we shall have an open mind, and not let a little bit of truth check the rush of the big truth, like a small rock does a railway truck. We get the small truth first. Good! We keep him, and we value him, but all the same we must not let him think himself all the truth in the universe."