This does not refer to a slip, a period of backsliding, a fall into temptation that you later regret. ‘Fall away’ is a very strong term in the Greek and in this case it refers to the complete rejection of God.
What is repentance? It is shame. Repentance is not just saying, ‘Oh Lord, I regret I have been a sinner, now give me heaven and salvation.’ What was missing in these lives was real shame, shame for outward sin, temper, lies; shame for my inward sin, pride, selfishness – the things we do, and the things we are. Shame means saying, ‘Oh Lord, I have not been under thy rule, under thy reign; I have pleased myself, I have ruled myself; deliver me from these things.’ It is not true repentance when a person says, ‘Forgive me, Lord’, and intends to do the same thing tomorrow. Maybe you have repented for one sin; you have not acknowledged that you are altogether a needy sin, needing the help and the cleansing provided only through Christ and Calvary. Repentance is the only way into the kingdom. It cannot be left out of any true presentation of the gospel. The seeker must ask God to give him repentance, ask God to give him shame for his sin, and a real sense of need of salvation. Are we making repentance a work as though a person has to accomplish deep sorrow before they can be accepted? No, we are not making it a work. Repentance is falling down before God. It is easy to fall down. When you fall down on your knees or you collapse on the floor, you do not say what a good thing that was, to be able to do that. There is no merit in that, but you must pass through that to find Christ. The leaving out of repentance by an evangelist will only lead to false conversions. Only the Spirit of God can give the gift of true repentance. If that is so, then we dare not blaspheme the Spirit, for if we do not genuinely repent we can never enter the kingdom of heaven.
We are not talking about somebody who has simply drifted away, who was once moved under the sound of the gospel and then just drifted away. Can that person be saved? Oh yes, the concern in that person's heart can be reignited. This is talking about the person who becomes an opponent of Christ, an enemy. This is about the person who has so dramatically rejected the gospel, that they slander Christ and oppose him, pour contempt upon him; it is as though they are crucifying him all over again. If somebody heard the gospel, was once concerned and has just wandered away and lived in the world and taken their lives to themselves, they can still be saved, but not if they become determined, militant, hostile enemies: that indicates a depth of rebellion that you cannot undo.
Why does the light they have received make such a difference? Why does it mean that God will not now forgive them? Why is true repentance now impossible? Because they have rejected Christ knowingly, and not in ignorance. Speaking of his pre-conversion persecution of believers, Paul says, I ‘was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief’ (1 Timothy 1:13). But these did not reject Christ in ignorance. They have understood real things under the influence of the Holy Spirit and yet they have offended and grieved the influence of the only one who can give them true repentance. It is Christ they have rejected, but it was the Spirit that was revealing Christ to them in a powerful and meaningful way.
Can believers fall from grace? Does this passage teach that a person can truly repent and yet fall away? We have already seen that it does not teach this, for the repentance seen here is not genuine. What this means is that a person can make significant advance in their understanding and can have real insight into the glory of Christ and the significance of his coming into the world and dying on Calvary for sinners. They can understand this much and still fall short of true conversion. The seeker should be fearful of failing to truly take hold of Christ. He or she cannot comfort themselves that they have begun to appreciate the gospel unless they have fully yielded to Christ; only then are they safe.
Is this the sin against the Holy Spirit? Yes, it is. It is given this name, because the Spirit has taught them real truth about Christ. God has set before them the most precious gift he has to give, and yet they have despised it and shown that they prefer instead what the world has to offer. There is such a thing as irresistible grace which is given to every one of the elect, chosen before the foundation of the world. But there is also such a thing as resistible grace which is given to some who are not chosen by God. These are allowed to resist the influence of the Spirit successfully, and they show how wicked is the human heart and how much we all need the overwhelming work of the Spirit of God in order to come to Christ.