The HolySpirit is the Lord who draws us to faith in Christ. Rejecting the wooing of the HolySpirit is offensive and is the signal that the rejecter is not worthy of Christ.
It is one thing to resist the HolySpirit. Many have done so and later been wooed by the HolySpirit and received Christ Jesus as Saviour.
However, to speak against the HolySpirit is to openly, verbally and orally deny His existence, His purpose or His authority. This is extremely serious because if puts a person on record before the Lord and man.
The Lord honours His Word and He honours our words as well. Mat 10:33