How we cite our quotes:
"You see, they should have […] known better
[…] my mother's sisters,
who said that I, Dionysus, was no son of Zeus" (1)
That's the understatement of the century. The fact that his mortal relatives deny that Dionysus is actually a god is the conflict brewing at the heart of the play. All the horrible blood and mayhem that we see is a result of this religious difference.
"I'm all ready, see,
complete in Dionysiac trappings.
And why not?
He's my own daughter's child" (8)
Wouldn't it be a little weird if one of your relatives was a god? That's the situation that old Cadmus is in. Here we see him embracing the new religion of his grandson. Unlike Pentheus and the rest of his family, Cadmus totally buys into the divinity of Dionysus. Of course, this doesn't help at all by the end of the play. He's punished too.
"She'd [Semele] had the nerve to name Zeus the Father
as her lover…What gall! What effrontery!" (21)
Notice that Pentheus is not blasphemous towards all gods. It's just Dionysus that he has a problem with. He is offended by the idea that Semele, his aunt and Dionysus' mother, was the lover of Zeus. Perhaps this shows a dedication to Zeus, the Greek king of the gods. In the Greek mind, however, it was important to pay homage to all gods, because anyone of them could deal out punishment.