Mortal Sin in Scripture: Blasphemy

Updated: Aug 15

By Luke Lancaster



Some Christians hold to the false teaching of eternal security. They will claim that Christians will never go to hell. However, Scripture teaches that Christians can lose the gift of eternal life. One such way is through the mortal sin of blasphemy. This is, according to the Catechism, "directly opposed to the second commandment. It consists in uttering against God - inwardly or outwardly - words of hatred, reproach, or defiance; in speaking ill of God; in failing in respect toward him in one's speech; in misusing God's name...It is in itself a grave sin" (CCC, para. 2148). Such a sin is seen in the teachings of Jesus and St. Paul, and in the examples of Judas and Peter.


Christ considered blasphemy to be a mortal sin. He said, “Whoever denies me before men, I also will deny before my Father who is in heaven” (Matthew 10:33).  Jesus was saying that, if a man claimed to be His friend, the man better not tell others that he have never heard of Jesus.  That would be nothing short of betrayal.  Jesus said that, when this person dies and is judged by God, Jesus would deny that He knew the man at all. This most likely implied Hell.  Jesus will treat his followers the way he is treated. 


Some might claim that this was hyperbole. They might say that Jesus was just using strong language about denying Him, but didn’t actually mean it literally.  Yet, the context of this passage shows that to be false, for Jesus spoke in no uncertain terms about Hell: "And do not fear those who kill the body but cannot kill the soul; rather fear him who can destroy both soul and body in hell” (Mt. 10:28).  Five verses before speaking of blasphemy, Jesus spoke of hell. Man really can go to Hell for blaspheming Christ in a serious way. 


St. Paul taught that blasphemy was a mortal sin, just like Jesus. He said, “…if we deny him, he also will deny us” (2 Tim. 2:12).  This is basically saying the same thing as Matthew 10:33. Those who deny Jesus will be denied by Jesus.


The apostle Judas committed the mortal sin of blasphemy when he denied Christ. Judas was chosen by Christ to be one of His twelve close friends and disciples (Mk. 3:19).  He and the other eleven were given “authority over the unclean spirits” (Mk. 6:7), and they went out together preaching that “men should repent” (Mk. 6:12), and even “healed” the sick with oil (Mk. 6:13).  He was not a fake Christian, but ministered to the people as a follower of Christ.  One day, though, he seriously messed up.  He went to the Jewish leaders who wanted to kill Jesus, and asked what would be offered to him if he told them where to find Jesus.  Thirty pieces of silver was offered.


Judas implied through his actions to the Jewish authorities: “I know the man, but I don’t want to anymore.”  Judas did not acknowledge Jesus before others as His friend (Mt. 10:32), but instead denied that Jesus was his friend (Mt. 10:33). To deny Jesus would result in Jesus denying the person before His Father (Mt. 10:32-33).  Judas sadly denied Christ through his actions.  Jesus and Judas were friends until the last supper where Jesus, knowing Judas agreed to betray Him, said, “He who ate my bread has lifted his heel against me.” (Mt. 13:18).  Judas broke bread with Jesus, and spent three years in close proximity to the guy, yet he lifted his heel in denial of Him.  Jesus actually quoted Psalm 41:9 to Judas, which fully reads, “Even my bosom friend in whom I trusted, who ate of my bread, has lifted his heel against me.”  Judas was a true believer in Jesus, yet committed the profound sin of giving Him up to death.  Remember, though, that he could have repented and apologized.


Not only did Judas fall into blasphemy, but Peter as well.  Peter, who was listed as one of Christ’s twelve close friends and disciples (Mk. 3:19), ruined his friendship with Christ.  When Jesus was on trial within the house of the Jewish high priest, Peter sat down outside around a fire with some people.  It was assumed that the man inside the house, Jesus, was a criminal, and nobody wanted to be associated with a criminal – including Peter himself.  And if somebody was a follower of the criminal, then they might face charges in court themselves. 


Peter's faith would be tested that night. He was an obvious follower of the supposed criminal on trial, for he was close to Jesus at nearly every significant event of his for the last three years. So, rather unsurprisingly, people began to question Peter.  When others noticed that he was a follower of Jesus, Peter would need to courageously say “yes, I do follow this guy.”  However, Peter sadly claimed to have never heard of the man.  Imagine the pain Jesus would have felt if He heard that.  Peter blasphemed not only once, but three times.


Peter fell into the same sin of Judas: blasphemy. As soon as Peter denied Him, Jesus “turned and looked at Peter” (Lk 22:61).  The expression on Christ’s face would’ve said, “I spent three years patiently teaching you, I planned to give you keys to My Kingdom - and this is how you treat Me?  Not only Judas, but you too?”  Catholics would call this action by Peter a mortal sin.  It was a sin so grave that Peter cut off fellowship with his Lord.  But as we know, that isn’t the end of the story like Judas, for Peter weeps, repents, and is reinstated (John 21:15-17).


Jesus taught that blasphemy would lead to rejection on judgment day. St. Paul echoed this teaching. Even two of Jesus's disciples fell into this sin. Both were in relationship with Christ.  Both were imperfect for their three years of travelling with Jesus. Yet it was the night of Jesus's arrest when they did something serious enough to shatter their friendship with Him.  One denied Christ in his actions gravely, and the other denied Him through his words gravely.