Almost forgot.
Catholic Answers puts out a nice little pamphlet titled “
Pillar of Fire, Pillar of Truth” that describes the main parts of our Faith.
This pamphlet (actually, a small 32-page booklet that is that many pages only because the paper it’s made on is small) is often given away for free but you can read the entire booklet here:
catholic.com/library/Pillar.asp
It covers what’s called the “Four Marks of the Church” – with scripture citations for each. Those 4 marks are One, Holy, Catholic, and Apostolic. You get those down, you pretty much got the definition of the Catholic Church. After each of these headings is a couple of brief paragraphs explaining why we Catholics see it this way.
The Church Is One (Rom. 12:5, 1 Cor. 10:17, 12:13, CCC 813–822)
The Church Is Holy (Eph. 5:25–27, Rev. 19:7–8, CCC 823–829)
The Church Is Catholic (Matt. 28:19–20, Rev. 5:9–10, CCC 830–856)
<here’s the text of that part of the pamphlet. I’m including it here in this post because it’s the most pertinent to the question that you asked.>
**Jesus’ Church is called catholic (“universal” in Greek) because it is his gift to all people. He told his apostles to go throughout the world and make disciples of “all nations” (Matt. 28:19–20).
For 2,000 years the Catholic Church has carried out this mission, preaching the good news that Christ died for all men and that he wants all of us to be members of his universal family (Gal. 3:28).
Nowadays the Catholic Church is found in every country of the world and is still sending out missionaries to “make disciples of all nations” (Matt. 28:19).
The Church Jesus established was known by its most common title, “the Catholic Church,” at least as early as the year 107, when Ignatius of Antioch used that title to describe the one Church Jesus founded. The title apparently was old in Ignatius’s time, which means it probably went all the way back to the time of the apostles. **
The Church Is Apostolic (Eph. 2:19–20, CCC 857–865)
Yup, we Catholics DO read the Bible.
Perhaps you could ask your girlfriend if you could go with her to Mass sometime, just so you can see what it is that we do when we go to church.
Hope this helps?
Your sister in Christ,
Veronica Anne (cradle Catholic since the 50’s)