Wll the first answer, of course, is the Holy Spirit.
I know my Dad had been praying for me for years, and I think that his (deceased) mother, who was a very holy woman, had been praying for me too.
In addition to that, there was John 17:21. I was completely unsatisfied with the Protestant concept of the “invisible unity of believers” because it does not, in the words of Jesus, help us become “perfectly one, so that the world may know that Thou hast sent me.” It doesn’t show the world any unity at all, and the Catholic Church is the only one that seems to think visible unity is even desirable. In any case there can’t be any unity without authority, so without a Pope, you see continued fractures, like in so many Protestant denomenations. I guess Jesus knew something about human nature.
Another was the concept of Mary having more children. I couldn’t find any Protestant explanation for why Jesus would give His mother to John if He had natural brothers. I heard a few attempts at explanation, but none that satisfied. It would be cruel, it would be rude, and it would be un-Jewish. I just can’t see it.
But really, I had been prompted by the Spirit to do some reading, like Scott Hahn. It helped me see that the reasons I had left the Church in the first place were based on false information. How could I reasonably reject Papal Infallibility without actually knowing what it meant? That sort of thing.
So that is a very abridged version of my story. But what brought it about, and I think probably all you can do about it, is prayer. Pray for your son to be open to the voice of the Holy Spirit and for his wife to be listening too. These “born again” churches are generally full of a lot of holy and kind people, who just happen to misunderstand the nature of the Church Jesus founded and its authority. Pray for them all.
Parents are, I think, pecularly poorly placed to talk about this to their adult children when they disagree, although I’ve had some really uplifting conversations with my Dad now that I’m back in the Church.
Your best bet it to do spiritual reading (especially since it is Lent), perhaps the writings of the saints or Church Fathers, and possibly the catechism, if it’s been a while since you read it. Then if he comes to you with questions or makes a false statement about the Churchin your presence, you will be prepared to say a quick prayer for guidance from the Holy Spirit and respond with the correct information.
If you get EWTN, you would probably find The Journey Home interesting and comforting. I really enjoy it. On the east coast it is at 8pm on Monday.
Best of luck, and I will pray for you all.
–Jen
Major props. Not everyone is a pre-Vatican II Catholic who wears a suit and tie every single day of the week (if anyone wears a suit to my funeral, i’m going to jump out of the casket and rip it off) and lone for the days of 1950’s-era entertainment.