What is Blasphemy against the Holy Spirit?

Matt 12:32 says "Anyone who speaks a word against the Son of Man will be forgiven, but anyone who speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come."

The blasphemy against the Holy Spirit is deliberate rejection of Christ and His salvation. It is the ultimate sin that by its very nature puts a man beyond the opportunity of salvation. This is because it is the Holy Spirit who brings the offer of salvation to the heart of man. Salvation is granted only upon a positive response to the His prompting. To reject Him is to act presumptuously and thus to blaspheme God. Those who reject His offer of salvation are in reality blaspheming the very nature of God Himself and the genuineness of His grace.

Owen Weber 2009