Taken from a study of Matthew 12:22-32, 1 John 5:16-16, and Hebrews 6:4-6, here is my proposed definition of the unpardonable sin. It is a single sin, quite visible to the unaided eye, committed only by professing Christians, only in the context of the visible church, involving repudiation of Christ by way of open contempt for and blasphemy of the Holy Spirit. After seeking to validate this definition, I then review several sins, which cannot be classified as unpardonable, based upon the biblical definition. In the end, the study shows the wonder of God's grace. Every conceivable sin is forgivable, except one.
