What is the “Unforgivable Sin”?

Last week’s Monday Morning Scripture post highlighted Jesus’ response to accusations that he was in league with the devil himself. In answering his critics, Jesus refers to something that has troubled Christians ever since: the so-called “unforgivable sin.” Here are Jesus’ words: http://cfb-christianfaithblog.blogspot.com/2013/05/the-unforgivable-sin.html