I don’t think I’ve ever met a Protestant who was not quite aware of the difference between a Catholic and a Protestant–well, except that they may imagine that incorrect things are the differences instead of the true things. At any rate, you can say, “We believe that a Christian has to be prepared to receive Holy Communion in the Church, a preparation which ends in full reception into the Church. It isn’t that we do not want you, but that we want all of you. If you have not yet joined the Church, we ask that you wait to receive Holy Communion until you do.”
You can also explain what the Mass is, with your ability to do so. Who knows, if they attend Mass having been given an understanding of what happens at Mass, they may want to join the Church. (I believe this is what happened to Scott Hahn.)
*…The second thing that happened was when I quietly slipped into the basement chapel down at Marquette, Gesu. They were having a noon Mass and I had never gone to Mass before. I slipped in. I sat down in the back pew. I didn’t kneel. I didn’t genuflect, I wouldn’t stand. I was an observer; I was there to watch. But I was surprised when 40, 50, 60, 80, or 100 ordinary folk just walked in off the street for midday Mass, ordinary folk who just came in, genuflected, knelt and prayed. Then a bell rang and they all stood up and Mass began. I had never seen it before.
The Liturgy of the Word was so rich, not only the Scripture readings. They read more Scripture, I thought, in a weekday Mass than we read in a Sunday service. But their prayers were soaked with Biblical language and phrases from Isaiah and Ezekiel. I sat there saying, "Man, stop the show, let me explain your prayers. That’s Zechariah; that’s Ezekiel. Wow! It’s like the Bible coming to life and dancing out on the center stage and saying, “This is where I belong.”
Then the Liturgy of the Eucharist began. I watched and listened as the priest pronounced the words of consecration and elevated the host. And I confess, the last drop of doubt drained away at that moment. I looked and said, “My Lord and my God.” As the people began going forward to receive communion, I literally began to drool, “Lord, I want you. I want communion more fully with you. You’ve come into my heart. You’re my personal Savior and Lord, but now I think You want to come onto my tongue and into my stomach, and into my body as well as my soul until this communion is complete.”
And as soon as it began, it was over. People stuck around for a minute or two for thanksgiving and then left. And eventually, I just walked out and wondered, what have I done? But the next day I was back, and the next, and the next. I couldn’t tell a soul. I couldn’t tell my wife. But in two or three weeks I was hooked. I was head over heels in love with Christ and His Real Presence in the Blessed Sacrament. It became the source and the summit and the climax of each day, and I still couldn’t tell anybody. *
catholiceducation.org/en/religion-and-philosophy/apologetics/the-scott-hahn-conversion-story.html