Recently, while on the road giving a workshop, I took the opportunity to go the Cathedral in that city for a Sunday Eucharist. I was taken aback by the homily. The priest used the Gospel text where Jesus says, I am the vine and you are the branches, to tell the congregation that what Jesus is teaching here is that the Roman Catholic Church constitutes what is referred to as the branches and the way we link to those branches is through the mass and if we miss mass on a Sunday we are committing a mortal sin and should we die in that state we will go to hell.
Then, aware that what he was saying would be unpopular, he protested that the truth is often unpopular, but that what he just said is orthodox Catholic teaching and that anyone denying this is in heresy. It's sad that this kind of thing is still being said in our churches.
Does the Catholic Church really teach that missing mass is a mortal sin and that if you die in that state you will go to hell? No, that's not Catholic orthodoxy, though popular preaching and catechesis often suppose that it is, even as neither accepts the full consequences.
Here's an example: Some years ago, I presided at the funeral of a young man, in his twenties, who had been killed in a car accident. In the months before his death he had for all practical purposes ceased practicing his Catholicism: He had stopped going to church, was living with his girlfriend outside of marriage, and had not been sober when he died. However his family and the congregation who surrounded him at his burial knew him, and they knew that despite his ecclesial and moral carelessness he had a good heart, that he brought sunshine into a room and that was a generous young man.
At the reception after the funeral one of his aunts, who believed that missing mass was a mortal sin that could condemn you to hell, approached me and said: "He had such a great heart and such a wonderful energy; if I were running the gates of heaven, I would let him in." Her comment wonderfully betrayed something deeper inside of her, namely, her belief that a good heart will trump ecclesial rules in terms of who gets to go to heaven and the belief that God has wider criteria for judgment than those formulated in external church rules. She believed that it was a mortal sin to miss mass on Sunday but, for all the right reasons, could not accept the full consequences of that, namely, that her nephew was going to hell. Deep down, she knew that God reads the heart, understands human carelessness, welcomes sinners into his bosom, and does not exclude goodness from heaven.
But that still leaves the question: Is it orthodox Roman Catholic teaching to say that it is a mortal sin to not go to church on a Sunday and that such an ecclesial lapse can send you to hell? No, to teach that categorically would itself be bordering on heresy.
Simply stated, Catholic moral theology has always taught that sin is a subjective thing that can never be read from the outside. We can never look at an action from the outside and say: "That's a sin!" We can look at an action from the outside and say: "That's wrong!" But that's a different judgment. From the outside we can judge an action as objectively wrong, but we can never make the judgment that it's a sin. Moreover this isn't new, liberal teaching, it is already found in our traditional Catechisms. Nobody can look at the action of someone else and say: "That's a sin!" To teach that we can make such a judgment goes against Catholic orthodoxy. We can, and must, affirm that certain things are wrong, objectively wrong, but sin is something else.
Probably the most quoted line from Pope Francis is his famous response to a moral question where he simply responded: "Who am I to judge?" He's in good company. In the Gospel of John, Jesus says: "You judge by appearances; I judge no one." That, of course, does not mean that there isn't any judgment. There is, it's real, and it can condemn someone to hell. But it works this way: God's Love, Life, Truth, and Light come into the world and we judge ourselves apposite them. God condemns no one, but we can condemn ourselves. It is God's Love, Life, Truth, and Light against which we weigh ourselves and these determine who goes where, already here on earth and in eternity.
In our catechesis and our popular preaching we must be more careful in our use of the term "mortal sin" and in our judgments as to who goes to heaven and who goes to hell, fully aware that there wasn't any group that Jesus was harsher on than on those who were making those kinds of judgments.