Matthew Series - The Unforgivable Sin

As the Pharisees continue to challenge Jesus, he teaches them about the power of words, and the power words have to reveal what's going on deep in our hearts. Within this lesson, he tells them something odd - those who speak against the "Son of Man" (or Jesus himself) will be forgiven, but those who speak against the Holy Spirit will not be forgiven. In fact, we are told that this is the "unforgivable sin." By why are words important and what is the significant of speaking against the Holy Spirit?