It’s literally blaspheming (speaking) against the Spirit, not merely “resisting” the Spirit or whatever.
The passage in Mark tells us why Jesus said that stuff about blasphemy against the Holy Spirit :
“Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith soever they shall blaspheme:
But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation.
Because they SAID, He hath an unclean spirit.”
Here’s a cross reference from Matthew and Luke that supports it: “Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men. And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.” “And whosoever shall speak a word against the Son of man, it shall be forgiven him: but unto him that blasphemeth against the Holy Ghost it shall not be forgiven.”
But I don’t necessarily think that someone saying a Christian has an “unclean spirit” or general blasphemy/blasphemy against God in general is necessarily blaspheming against the Spirit if the person didn’t know anything about the Spirit when they said that and they’re not directly blaspheming specifically against the Spirit.
I believe it’s when people are aware and consciously blaspheming specifically against the Holy Spirit is when it’s unforgivable. Like if someone accidentally insulted your loved one or not fully knowing/indirectly they insulted your loved one, then it is forgivable, but when someone literally consciously knowingly insults your loved one specifically is when there is offense. The blasphemers knew they were blaspheming against God’s Spirit. See the people’s remarks: “And all the people were amazed, and said, Is not this the son of David?” Even though these people were common people and not “learned” (like the religious leaders) it was so clear what’s going on even the common people (Jews) attribute this to God… (Son of David, the Messiah)…so how much more is this clear to the “learned” people?
(They have no excuse, see even one of their own: Nicodemus’s reaction to Jesus’ miracles in John. Jesus wasn’t some heretical preacher doing miracles, especially when He’s also using Scripture and common sense to back Him up.)
Also, with regards to “learned”, Jesus pointed out: “And if I by Beelzebub cast out devils, by whom do your children cast them out? therefore they shall be your judges.” (Rhetorical question from Jesus, and they knew the answer being religious leaders and who were not unfamiliar with the words and works of Jesus.) They knowingly and intentionally were speaking a word against both Jesus and the Spirit by which He did that miracle.
Plus, they were hardened against God (refusing to acknowledge the truth despite many signs, miracles, scriptural proofs pointing to the truth), which means:
A) This is not an ignorant act by an ignorant person.
B) This isn’t even an intentional act by an ignorant person.
C) The blasphemy is definitely intentional and specific against the Spirit through which Jesus had done the miracles in.