"It is a matter of great importance pastorally that we can say with absolute confidence to anyone who is overwhelmed by the fear that he has committed this sin, that the fact that he is so troubled is itself a sure proof that he has not committed it." (Qtd. Wilkins, Matthew: The New NIV Application Commentary, 449).
"[A]ny person who is genuinely worried about having committed the unforgivable sin against God, by virtue of this concern, can hardly be guilty of such blasphemy or denial." Matthew, vol 1, p.348.