How do I show a non practicing catholic that he ought go to church? When I invited him back to mass he said in so many words that by grace he is saved not works, like going to mass and participating in the sacraments.
Is it possible that your friend simply doesn’t want to go to church (because he thinks its boring, he would rather stay in bed or watch TV, etc.)? If so, then rational explanations of the importance of going to Mass and participating in the sacraments may not have much of an impact on him. Still, I think it is a noble effort on your behalf to give it a shot.
It sounds like he has a pretty loose idea of what a “work” is. Ask him how grace enters into our souls, and whether or not we have to do anything on our part in the process. If he says that we don’t have to do anything, and that grace is automatically placed within us, then, consequently, this means that everyone is automatically saved. But the Bible clearly teaches that there are those who will
not be saved.
If he admits that we are, indeed, expected to “do” something in the process of receiving and benefiting from grace (such as believing in Jesus, being a good person, etc.), then the things he says we must “do” are still works (at least in the general sense of the term). Then you can ask him why the works he says we must do are better than the sacraments that Jesus gave to the Church expressly for the purpose of conveying grace in very powerful ways.
Also, if the things that he says we must do also allow for him to stay at home goofing off, while the thing he says that have no value are the things that require someone to go to church, then this indicates that he is probably just looking for excuses not to go to church. If you notice this, then maybe you can point it out to him and see if he’s willing to discuss the real issue at hand.