It's not vague at all.
It's calling the Holy Spirit, the devil.
24 Now when the Pharisees heard it they said, “This fellow does not cast out demons except by Beelzebub, the ruler of the demons.”
25 But Jesus knew their thoughts, and said to them: “Every kingdom divided against itself is brought to desolation, and every city or house divided against itself will not stand. 26 If Satan casts out Satan, he is divided against himself. How then will his kingdom stand? 27 And if I cast out demons by Beelzebub, by whom do your sons cast them out? Therefore they shall be your judges.28 But if I cast out demons by the Spirit of God, surely the kingdom of God has come upon you. 29 Or how can one enter a strong man’s house and plunder his goods, unless he first binds the strong man? And then he will plunder his house. 30 He who is not with Me is against Me, and he who does not gather with Me scatters abroad.
31 “Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men.32 Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come.
Matthew 12:24-31
blasphemy against the Spirit, is calling the Holy Spirit, the devil.
JLB