Question: Is it possible for a Believer to Commit the unforgivable sin?
Answer: The unforgivable sin is widely misunderstood. Let’s explore.
I had a Bible professor who said something very profound once… well I’m sure she said profound things all the time, but I remember this one. A student was trying to prove a point; he only had one verse to back up his claim, and it was a pretty cryptic verse at that. She said:
“We don’t build good theology on of one verse, especially when it’s not clear what the verse means.”
I’ve often thought back to this concept when someone is trying to make a case for some theological idea, and basing it on one or two verses.
I have often made the case that even if a person believes in Jesus for salvation but then stop believing, they are still saved. If you’re not familiar with this concept, I’d encourage you to read the above articles.
When the Once Saved Always Saved discussion comes up it’s very common for someone to claim that the unforgivable sin proves that a person can lose their salvation.
But does the unforgivable sin prove that one can lose their salvation?
Well to start with, Jesus wasn’t talking to people who had salvation when he mentioned the unforgivable sin. Instead he was talking to the Pharisees who were in the process of rejecting him. So, even if we completely understood what the unforgivable sin is it still couldn’t be used to prove that salvation could be lost, since Jesus never ever ever ever mentions that a saved person is in danger of committing an unforgivable sin. He only talked about the unforgivable sin to unbelievers. That’s a huge red flag.
“If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.” (1 John 1:9)
— for they were saying, “He has an unclean spirit.” (Mark 3:29-30)
That’s it! That’s the entirety of what is said about the unpardonable sin. We have some context and two mentions of it in the entirety of scripture. Is that enough to build a robust theology on? In my opinion, no.
So what do we know about it? Well, not much. It’s not clear exactly what the blaspheme of the Holy Spirit is. It has to do with denying the source of Jesus’ miracles. It has to do with denying that the Spirit is authenticating Jesus.
So, if that’s all we knew about it, we would have to say the blaspheme of the Holy Spirit could only take place while Jesus was on Earth performing miracles.
One of my favorite statements from a Biblical Scholar on the unforgivable sin comes from Louis Barbieri. Here’s what he says:
They were about to attribute incorrectly to Satan the power of the Holy Spirit exercised through Jesus and thus to commit the blasphemy against the Spirit. This specific sin cannot be reproduced today, for it required Jesus’ presence on earth with His performing miracles through the Spirit’s power. 
Beyond this, Jesus brushed the fear of the unforgivable sin away for anyone who believes in him. He showed that the unforgivable sin and believing in Jesus are mutually exclusive. That’s important. If someone ever believes in Jesus for salvation at any point in their life, they can never commit an unforgivable sin. That’s because Jesus said:
So for any who have believed in Jesus for salvation, there is an absolute promise of eternal life. The person who has that life will never lose it. They will never do anything that can get them snatched out of the hand of God. There is no unforgivable sin for the person who has believed in Jesus.
“ I give them eternal life and they will never perish…”
“I give them eternal life and they will never perish unless they do the unforgivable sin.”
Why do people cling to two unclear verses about the unforgivable sin and reject dozens of clear verses about salvation?
I think it’s because telling someone else that they are going to Hell offers a certain thrill. It’s a grievous thrill, but it’s a thrill none the less. The sin of legalism and judgmentalism is attractive to the self-righteous. There are many who believe themselves to be righteous, and they want to point at others who are less righteous and tell them they are going to go to Hell.
It simply does not fit with the character of Jesus. He spent his ministry offering people a way out of Hell.
Let me leave you with this. Jesus said:
 Louis A. Barbieri, Jr., “Matthew,” in The Bible Knowledge Commentary: An Exposition of the Scriptures, ed. J. F. Walvoord and R. B. Zuck, vol. 2 (Wheaton, IL: Victor Books, 1985), 47.