In studying Hebrews with high school students in their New Testament Survey class, we looked at Hebrews 6:4-6 and discussed the unpardonable sin:
For in the case of those who have once been enlightened and have tasted of the heavenly gift and have been made partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, and then have fallen away, it is impossible to renew them again to repentance, since they again crucify to themselves the Son of God and put Him to open shame. (NASB)
In the Greek, the highlighted word "impossible" found in verse 6 in the NASB is actually the first word of verse 4 (the KJV and ESV render it this way) and is placed at the beginning for a warning emphasis. Certain actions can render a person unable to repent.
This same emphasis is seen later in Hebrews 10:26, where in the Greek the word translated "willfully" (or "deliberately") is placed at the beginning in the original Greek text:
For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins.
The author of Hebrews wanted to capture the attention of his readers who were in danger of drifting away from the faith. Be careful, he is telling them, for you are in danger of falling into sin that will not be forgiven. What then is that sin?
As Jesus makes clear, it is the blasphemy of the Holy Spirit.
Therefore I say to you, any sin and blasphemy shall be forgiven people, but blasphemy against the Spirit shall not be forgiven. Whoever speaks a word against the Son of Man, it shall be forgiven him; but whoever speaks against the Holy Spirit, it shall not be forgiven him, either in this age or in the age to come. (Matthew 12:32; also see Mark 3:29 where Jesus calls this an “eternal sin;” also Luke 12:10)
A careful study of the Scriptures brings further clarifications regarding this sin.
Those outside the knowledge of the gospel cannot commit the unforgivable sin. Certainly their ignorance is not bliss, but neither is it ultimately damnable. People can blaspheme Jesus, and still be forgiven. Such was the case of the Apostle Paul.
Rather, the unforgivable sin is one committed by people in the know, i.e., those who are experiencing the presence of God. The example in the gospels of the Pharisees shows that they had seen Jesus’ miracles, heard his teaching, and, in the light of that knowledge, rejected Christ and called his work satanic. Similarly, people in the church can fall into this sin as J.I. Packer points out in his Concise Theology:
It is possible for people to be enlightened to the point of knowing inwardly that Jesus is the divine Savior he claims to be, and still not be willing to admit it publicly, because of all the behavioral changes that such an admission would make necessary…Callousing one’s conscience by dishonest reasonings so as to justify denial of God’s power in Christ and rejection of his claims upon one is, then, the formula of the unpardonable sin.
Like signs warning "Danger: Bridge Out Ahead," we see carefully placed throughout the Scriptures warnings to those in the church about ultimate failings (see Numbers 15:30-31 and I John 5:16 for other texts; study the life of Judas Iscariot as an example). As I told my students, these warnings are there because "though we speak in this way, yet in your case, beloved, we feel sure of better things - things that belong to salvation" (Hebrews 6:9). We discussed that it takes steps to get to the point of the unforgivable sin, so we should examine our lives and make sure we are not walking in that direction.
Perhaps there is no better illustration of this sin, the weaving together of Scriptures concerning it, and the self-examination that should come in considering it than Bunyan's story of the man in the iron cage in the house of the Interpreter. Read it below and, as the Interpreter says, "Let this man's misery be remembered by thee, and be an everlasting caution to thee."
Now, said Christian, let me go hence. Nay, stay, said the Interpreter, till I have showed thee a little more, and after that thou shalt go on thy way. So he took him by the hand again, and led him into a very dark room, where there sat a man in an iron cage.
Now the man, to look on, seemed very sad; he sat with his eyes looking down to the ground, his hands folded together, and he sighed as if he would break his heart. Then said Christian, What means this? At which the Interpreter bid him talk with the man.
Then said Christian to the man, What art thou? The man answered, I am what I was not once.
CHRISTIAN: What wast thou once?
THE MAN: The man said, I was once a fair and flourishing professor, both in mine own eyes, and also in the eyes of others: I once was, as I thought, fair for the celestial city, and had then even joy at the thoughts that I should get thither.
CHRISTIAN: Well, but what art thou now?
THE MAN: I am now a man of despair, and am shut up in it, as in this iron cage. I cannot get out; Oh now I cannot!
CHRISTIAN: But how camest thou into this condition?
THE MAN: I left off to watch and be sober: I laid the reins upon the neck of my lusts; I sinned against the light of the word, and the goodness of God; I have grieved the Spirit, and he is gone; I tempted the devil, and he is come to me; I have provoked God to anger, and he has left me: I have so hardened my heart, that I cannot repent.
Then said Christian to the Interpreter, But is there no hope for such a man as this? Ask him, said the Interpreter.
CHRISTIAN: Then said Christian, Is there no hope, but you must be kept in the iron cage of despair?
THE MAN: No, none at all.
CHRISTIAN: Why, the Son of the Blessed is very pitiful.
THE MAN: I have crucified him to myself afresh, I have despised his person, I have despised his righteousness; I have counted his blood an unholy thing; I have done despite to the spirit of grace, therefore I have shut myself out of all the promises and there now remains to me nothing but threatenings, dreadful threatenings, faithful threatenings of certain judgment and fiery indignation, which shall devour me as an adversary.
CHRISTIAN: For what did you bring yourself into this condition?
THE MAN: For the lusts, pleasures, and profits of this world; in the enjoyment of which I did then promise myself much delight: but now every one of those things also bite me, and gnaw me like a burning worm.
CHRISTIAN: But canst thou not now repent and turn?
THE MAN: God hath denied me repentance. His word gives me no encouragement to believe; yea, himself hath shut me up in this iron cage: nor can all the men in the world let me out. Oh eternity! eternity! how shall I grapple with the misery that I must meet with in eternity?
INTERPRETER: Then said the Interpreter to Christian, Let this man's misery be remembered by thee, and be an everlasting caution to thee.
CHRISTIAN: Well, said Christian, this is fearful! God help me to watch and to be sober, and to pray that I may shun the cause of this man's misery. Sir, is it not time for me to go on my way now?