One thing that stands out to me about Jack Seward as a character is that he is generally very aware of his own weaknesses and tends to mitigate for them.
Van Helsing's assessment of Jack Seward:
"You are 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? [...] Dr Seward's diary, 26 September
Jack Seward's assessment of Van Helsing:
He is a seemingly arbitrary man, but this is because he knows what he is talking about better than any one else. He is a philosopher and a metaphysician, and one of the most advanced scientists of his day; and he has, I believe, an absolutely open mind. This, with an iron nerve, a temper of the ice-brook, an indomitable resolution, self-command, and toleration exalted from virtues to blessings, and the kindliest and truest heart that beats—these form his equipment for the noble work that he is doing for mankind—work both in theory and practice, for his views are as wide as his all-embracing sympathy. Letter from Dr. Seward to Arthur Holmwood - 02 August
While unable (for the moment at least) to emulate Van Helsing's open mindedness, he does admire it, and he deliberately brought in someone who would be able to see possibilities he couldn't.
