Praised be Jesus and Mary, now and forever.
There are six sins against the Holy Spirit: presuming on God's mercy, despairing of God's mercy, willfully envying the good that God does to others, opposing known truth, obstinately remaining in sin, and final impenitence. These are terrible sins, unforgivable sins, as our Lord says, because they're a rejection of God's forgiveness. Unforgivable because they reject forgiveness. Today's gospel, the rejection of God's forgiveness, although He's evidently a prophet and more than a prophet, yet He's rejected in His own native place, makes me think of these terrible sins against the Holy Spirit. 
Now, the faithful sometimes worry, and rightly so; we should always be vigilant, but the faithful sometimes worry that they commit sins against the Holy Spirit, and this worry, this concern, this dread of the sins against the Holy Spirit is already a good sign that they're not committing them. To dread these sins, to be worried about them, to be vigilant about them, is already a sign you're not committing them. 
But there's an even better sign, a surer sign, and that is love for Our Lady. Why? Because it is impossible to love Our Lady and at the same time offend the Holy Spirit, her spouse. Our Lady is the spouse of the Holy Spirit. In fact, the more we love Our Lady, the more the Holy Spirit finds devotion to Our Lady in our souls, the more He hurries there, the saints tell us. St. Louis de Montfort, St. Maximilian. If the Holy Spirit finds Mary in our souls, He hurries there. He fills our souls. He stays there. He doesn't go away.
The best way to have devotion to the Holy Spirit is to have also devotion to His beloved spouse, Our Blessed Lady.
So again, these sins against the Holy Spirit are possible. We shouldn't have anxiety about them, especially if we love Our Blessed Lady. Have devotion to Our Lady. Love her. Surrender to her. Beg her to never allow you to offend the Holy Spirit. And be at peace.
And pray for those who are so blind that they don't even see that they're in sin against the Holy Spirit. That's the scary category. Pray for those. Make reparation for them.
Praised be Jesus and Mary, now and forever.