And that would make sense in that rejection of Jesus is not forgiven. And blasphemy against the Holy Spirit is identified as the one sin that is not forgiven.
The other alternative is that because the Holy Spirit's prompting is required to reach the point where you accept Jesus, that blaspheming the Holy Spirit can create a situation where you will never come to acceptance of Jesus, because the Holy Spirit will not prompt you.
For the record, I believe the first alternative, not the last.
Also, the context in which Jesus made that statement is when He was accused of casting out demons by Satan’s power. It’s logical to assume that blasphemy of the Holy Spirit would be attributing God’s work to Satan or Satan’s work to God.
However, consider Paul. Paul who was running around the country killing Christians in the name God. Yet God went out of His way to convert Paul and save him. You would think Paul had committed that form of blasphemy. So again, I come back to thinking that blasphemy against the Holy Spirit is continued rejection of Jesus.
In conclusion, if you are tempted to say anything that might be blaspheming the Holy Spirit, DON’T! And if you are prompted to accept Jesus as Savior, DO IT!.