Out of curiosity, how exactly does one sin against the Holy Spirit? I've heard of the concept, but always in a context that assumed the listener knew what such a sin entailed.
By denying the Holy Spirit. By denying Christ. By denying the holiness of Mary, the Mother of God. By denying the holiness of the saints. . By deny the Catholic Church. By denying the Apostles and St. Peter as the first Bishops and the first Pope.
And many other things
By denying Christ and EVERYTHING connected with him.
Most theologians agree that final impenitence is the real "blasphemy against the Holy Spirit".
In context, Jesus was talking to the Pharisees, who were attributing his preaching and miracles to demons. He's saying, in effect, "If you're this hardened in evil -- that you attribute my miracles to demon -- then you are so hardened in evil that you will not accept the grace of final repentance at your death, and are certain to go to hell".