Quote 4
"You know, dear, my ideas of the trust between husband and wife: there should be no secret, no concealment." (9.2)
This is Jonathan Harker's ideal of marriage. Of course, he's the one who breaks this ideal when he stops keeping Mina in the loop about their fight against Dracula. And look what happens! She gets bitten.
Quote 5
There are many odd things to put down, and, lest who reads them may fancy that I dined too well before I left Bistritz, let me put down my dinner exactly. I dined on what they call "robber steak" […] The wine was Golden Mediasch, which produces a queer sting on the tongue, which is, however, not disagreeable. I had only a couple of glasses of this, and nothing else. (1.17)
Jonathan Harker assures any future readers of his diary that he wasn't drunk the night he traveled to Castle Dracula. He anticipates that some people might assume that he was hallucinating or in an alcohol-induced haze when they read about the "blue lights" and the wolves, so he tells us exactly what he had to eat and drink beforehand.
Quote 6
[…] I fell to at once on an excellent roast chicken. This, with some cheese and a salad and a bottle of old Tokay, of which I had two glasses, was my supper. (2.18)
Again, Harker is careful to tell us exactly what he had to eat and drink—maybe he's anticipating, again, that future readers of his diary might assume that he was hallucinating the strange things he witnessed at Castle Dracula.