
(Image by José Luiz.)
Compare Matthew 7:16-20; Luke 6:43-45; 12:10
These are the passages indicating that, while blasphemy against Jesus can be forgiven, blasphemy against the Holy Spirit cannot.
Latter-day Saints typically take the word against here in somewhat different senses: To say a word against Jesus is to deny propositions about him, whereas to say a word against the Holy Spirit is to override what the Spirit is saying, to contradict the Spirit. And the Spirit isn’t speaking self-referentially, but of Christ. The distinction is somewhat fuzzy, as, in both cases, saying a word against them is denying what they say. But the idea seems to be that the Holy Spirit conveys truths to us in a way that is more powerful than merely hearing the mortal Jesus say something, and that contradicting the declarations of the Spirit is, therefore, more seriously culpable.
Of course, these passages also set forth the important principle of judging religious claims by their effects, by their fruits.