There IS an Unforgivable Sin
Blasphemy of the Holy Spirit
By one interpretation, this is Persistent Denial
of the Holy Spirit's Work in our hearts
http://www.bibleinfo.com/en/questions/why-blasphemy-against-holy-spirit-unpardonable-sin
A Christian that persistently denies the
work of the Holy Spirit is in Mortal Danger
So say you. What does Scripture say in the New Covenant?
I am merciful to their unrighteousness, and their sins and their iniquities I remember no more.Hebrew 8:12
And their sins and iniquities I remember no more.Hebrew 10:17
Christ first mentions it when dealing with persons who said that Christ’s miracles were done by the power of Satan. That was the context in which the blasphemy of the Holy Spirit was first spoken of in the Bible.