They accused Jesus of "having" the devil. Jesus answered that you can not plunder a strong man's house, unless you first bind the strong man. And then Jesus talks about blasphemy against the Holy Spirit.

If Satan is the strong man, this can mean that unless Jesus binds Satan first, Jesus can not cast out demons. "How can Satan cast out Satan?"

But the opposite can also be true? Before you say something evil against something you know is good, you first have to deliberately bind the knowledge of good inside you.