The foreign threat
Dracula comes from the east, buys property in England, and plans to blend into London society. The novel frames him as an invader who exploits English openness and law. Victorian readers would have recognized anxieties about immigration and empire in this setup.
Female sexuality and danger
Both Lucy and Mina are threatened by Dracula, but the novel treats them differently based on how sexually forward they seem. Lucy, who is flirtatious and has multiple suitors, becomes a vampire and is destroyed. Mina, who is dutiful and domestic, is saved. The pattern is not subtle.
Science versus the supernatural
The male characters are doctors, lawyers, and men of reason. They struggle to accept that vampires exist because their entire worldview says they cannot. Van Helsing forces them to take folklore seriously, and the novel suggests that pure rationalism leaves people defenseless against certain kinds of evil.
Collective action against individual evil
No single hero defeats Dracula. The group survives because they share information, pool resources, and trust each other. Dracula, who operates alone and through manipulation, is ultimately outnumbered by people who cooperate. Stoker makes teamwork the actual weapon.
The power of recorded knowledge
The characters win partly because Mina compiles their diaries and letters into a single document. Writing things down, organizing information, and sharing it gives the hunters an edge. The novel itself is that document, which makes the theme self-referential.