9 First then, I pray you to consider and understand that the Lord did not say, “No blasphemy of the Spirit shall be forgiven,” or, “whosoever speaks any word whatsoever against the Holy Ghost, it shall not be forgiven him;” but “whosoever speaks a word;” for had he said the former, there would have remained to us no subject of disputation at all. Since if no blasphemy, and no word which is spoken against the Holy Ghost, shall be forgiven unto men; the Church could not gain any one out of all the classes of ungodly sinners who gainsay the gift of Christ, and the sanctification of the Church, whether Jews, or heathens, or heretics of whatsoever sort, and some even of little knowledge in the Catholic Church itself. But God forbid that the Lord should say this: God forbid, I say, that the Truth should say that every blasphemy and every word which should be spoken against the Holy Ghost, has no forgiveness neither in this world, neither in the world to come.
Source: Sermons on Selected Lessons of the New Testament (New Advent)