'By three they come, by three the way opens' one of the characters says in the Diablo 4 cinematic.

Blood, whether we're talking about vampirism or not, is ritualistically and literally a life force Catholics consider the sacramental wine the blood of Christ, for example. Opening the door to the inner sanctum in the cinematic also requires a blood sacrifice. Vampire lore (or Greco-Roman mythology) also considers her the starting point for vampirism-hence why bringing Lilith back from her prison in Diablo 4 would require a blood sacrifice. In Jewish mythology, it's been said that Lilith was Adam's first wife.

There are many parallels between the Diablo Lilith and the mythological Lilith.

Much of her fictional backstory in Diablo is from Jewish mythology and folklore (although the same passages in the Hebrew Bible about her also appear in the many versions of the Christian Old Testament). In the Diablo 4 trailer, Lilith is brought back from the Void, and she looks just as pissed off as the day she was banished there.

Diablo iv by three they come characters