I would recommend this, from a little bit of experience.
When I was anti-Catholic, folks used to try to argue the entire reformation all over again with me. This never worked, because each point was dilluted. It also didn’t work because of the fact that doctrines like faith alone and the symbolic presence of Christ were just too important for me to seriously consider any arguements about. What got to me was when I was introduced to a very minor, relatively inconsequential idea that was not only less important, but also much smaller in scope. Once I saw that the Catholics were right on that point, it made me a LOT more interested to pay attention to evidence for other points.
That one minor thing for me was the practice of calling priests father. What really got me was something very, very simple. Someone showed me all the places in the Bible where it shows that the Apostles were called spiritual fathers:
[quote=Me on a website of mine]The Apostles were called Father all the time, and they called those in the congregations (like Ephesus, Galatia, Corinth, etc.) they had started child, son, and daughter. You can see this just by opening up your Bible:
§ 2 Timothy 1:2 - “To Timothy, my beloved child: Grace, mercy, and peace from God the Father and Christ Jesus our Lord” (Paul as Father)
§ 2 Timothy 2:1 - “You then, my son, be strong in the grace that is in Christ Jesus” (Paul as Father)
§ Philemon 10 - “I appeal to you for my child, Onesimus, whose father I have become in my imprisonment” (Paul as Father)
§ 1 Peter 5:13 - “She who is at Babylon, who is likewise chosen, sends you greetings; and so does my son Mark” (Peter as Father)
§ 3 John 4 - “No greater joy can I have than this, to hear that my children follow the truth” (John as Father)
§ Also 1 Corinthians 4:17, 1 Timothy 1:2, 1 Timothy 1:18, Phillipians 2:22, Titus 1:4, 2 Corinthians 12:14, Galatians 4:19, 1 John 2:1, 1 John 2:13-14.
§ And Especially 1 Corinthians 4:14-15 - “I do not write this to make you ashamed, but to admonish you as my beloved children. For though you have countless guides in Christ, you do not have many fathers. For I became your father in Christ Jesus through the gospel” (Paul as Father)
Jesus’ statement not to call anyone Father is hyperbole, the same as his statement to pluck out our eyes if they cause us to sin. He’s just making a point. If he really meant not to call anyone a biological father (like our dads) or a spiritual father (like our priests), then Paul, Peter, and John would not have done so.
It was very simple, very quick, and very straightforward. What’s more, it really hit home because I had always believed that, “well, you can argue with me on the real presence, or on this or that, but the instruction to call no man father is SOO straightforward and solid that the Catholics just can’t defend it in a million years.” Nevertheless, seeing those few scripture verses made me realize that the Apostles were known as fathers, so not only did it show me that the Church was right on this point, but it showed me that I had to take an entirely different approach to interpreting Scripture. It made me realize that the method of taking verses as literal instructions direct to me just didn’t work.
So I’d recommend studying up on this topic and approaching him with this, nothing else. Try to get him to see this, then wih any luck he’ll be curious for more.