I ran into a New Order man hoping to be a deacon one day. He asked me if I had ever been to Jerusalem. Well, he has and he told me there was the Our Father in all languages and to his surprise he found that all religions have the Our Father is common. And that Christ came for one thing, "Love".
Oh, don't you just love it! I listened and ask the Holy Ghost to help out. I said, it is Christ Precious Blood that brings us together and with it we can enter Heaven, our white garb. That is Love. The other religions have no sacrament/Precious Blood. So, if we are united as you say with the Our Father then as St. Paul would say, "He came in vain, then.
You gave a very good answer to your friend, the Holy Ghost was with you. I have found that basic catechism can answer questions or statements from those who are in error.