Jesus was accused of blasphemy which was punishable by stoning. It was a serious crime then and it is for us today also a very grave sin. Sadly it is all too common for us to hear people uttering blasphemous words and sentiments in everyday speech; we need to be very careful indeed about our own speech with this regard because we can easily put ourselves out of a state of grace.
Because of its gravity and because it is so common, we need to be clear what the sin is and what to do if we commit it.
You shall not take the name of the Lord your God in vain. Ex 20:7; Dt 5:11
Blasphemy is a sin against the love of God and opposes the second commandment. It is any uttering against God. This uttering can be silent and within, as well as audible. And it does not affect the gravity of the sin whether others can hear it or not. Any words of hatred, reproach or defiance against God are blasphemy. It can be speaking ill of God. It can be failing to respect God in one’s speech. And of course blasphemy is misusing the name of God, not least in a curse.
Blasphemy also extends to language against Christ’s Church, against the Saints, and against sacred things or places. It is also blasphemous to use God’s name to cover up criminal practices, to reduce people to servitude, to torture persons or put them to death. Blasphemy is contrary to the respect and honour due God and His holy name.
Blasphemy is intrinsically a grave sin. Some sins are intrinsically grave, and this means that whatever the circumstances are, and whatever the motives for sinning are, it is an act which in and of itself is gravely sinful. We cannot talk our way out of it!
So blasphemy’s intrinsic gravity means that if we commit that sin knowing it is sinful and we were not pressurised* into it, we have committed mortal sin. By this sin we have cut ourselves off from God, turned away from Him and destroyed charity in our heart. In the state of mortal sin we can only be brought back by a new initiative of God’s mercy – that is, through the sacrament of Penance. In the state of mortal sin we may not receive the Blessed Sacrament of the Altar without bringing condemnation on ourselves and committing sacrilege.
If we realise we are a blasphemer we need to repent as soon as possible and we need to get to confession regularly until we have driven the habit out of our system.
We live in a time and place where God and His Holy name is regularly profaned, but for those without faith there is ignorance to defend their action. For those of us with faith, we have no such defence. God’s Holy name is for salvation not for cursing – by profaning His holiness and His sacred name we curse no one but ourselves.
See also the article in the Catechism: CCC 2142f.
* Pressure can come for example from peers or from bad habits. If we have laid down a habit of blaspheming over a long period of time while the first times we blasphemed might have been mortal sins, now because of the habit, the sin though grave is not a mortal sin. However recourse to the sacrament of penance is the best course of action after committing blasphemy.