The type of sin referred to in 1 John 5:16 is comparable to the “unforgivable sin” mentioned by Jesus in Mark 3:28-29 (associated with “blasphemy of the Holy Spirit”).
Whatever Jesus is talking about must be understood in light of the wider New Testament teachings about sin and forgiveness. For example, God’s heart toward our sin is clearly shown in Jesus’ words on the cross: “Father, forgive them, for they do not know what they are doing” (Luke 23:34). God’s desire to forgive is proclaimed in I John 1:9, “If we confess our sins, he who is faithful and just will forgive us our sins and cleanse us from all unrighteousness.” So, if this is God’s heart for forgiveness, why does Jesus speak of an “unforgivable sin?”
First we need to be clear on the context and understand what Jesus is and is not saying in this passage. Jesus makes his statement in response to the Jewish religious leaders’ claim that Jesus was casting out demons by the power of “Beelzebul” (another name for Satan). Notice that Jesus doesn’t explicitly say that the religious leaders committed blasphemy of the Spirit. Rather, it seems that Jesus is warning them about the deceptive path they are on.
In the parallel passage in Matthew, Jesus explains that, “it is by the Spirit of God that I cast out demons” (Matt 12:28). In this context, the religious leaders were essentially identifying the Holy Spirit with the evil spirit, Satan himself. This gives us insight into why this type of sin is unforgivable. It is not that God arbitrarily picks one sin that he refuses to forgive! Rather, it is the nature of this sin that makes it unforgivable. This sin involves such deep spiritual hardness of heart that the person is willingly equating the Spirit of God with the spirit of Satan (“Beelzebul”).
It is important to remember that in Jewish and early Christian apocalyptic thought, the Holy Spirit was understood to be the source of power and the chief “sign” that the Kingdom of God had dawned. For someone to willingly confuse the sign and power of the Kingdom of God with that of the kingdom of darkness revealed a heart that had willingly hardened itself beyond the point of redemption.
With this background in mind, we can return to 1 John 5:16. Apparently there is a type of sin that reveals a human heart to be exceptionally hardened against God and his offer of forgiveness. As with everything that Jesus taught, relationship with God always comes down to a matter of the heart.
