I was baptized Catholic as a child, attended Catholic school for 12 years and Mass my entire life, married a Catholic and am doing my best to raise 2 Catholic faithful children. However, the Catholic schools and churches where we live are surprisingly non-faith filled and are turning out agnostic kids left and right. To supplement our Catholic faith, we often go to bible study Wednesdays and Sundays at the 1st Baptist Church in our area. We have been doing this for over a year, so I feel pretty qualified to answer this question.
They say: Mutual Fellowship.
What they mean: YOU must denouce your Catholic Faith: Mary, the Saints, the Pope, the Eucharist, Confession, The Rosary, Advent, Lent, Stations of the Cross… all of it - out the door & become Baptist. (which will mean getting re-baptized because they don’t belive your first baptism meant diddly).
This is simply not true!
All of the Baptist in my Bible study, including the Pastor, know that we are Catholic, and attend Catholic mass weekly, and they still believe that we are “saved & born again”. In their opinion, Jesus came to earth to save us, and not to start a religion. Therefore, anyone who gets hung up on what religion are you, is missing the point entirely.
The issue they have with Mary & the Saints is their misinterpretation of our prayers to them. The second commandment talks against idle worship, and because they see Catholics creating images and praying seemingly to them, they think this is a sin. When I explained that our prayers are to the Mary and the Saints asking them to pray to God for us through intersession, they understood this, and were less judgemental about it. Ditto for the rosary, Stations of the Cross, or images and icons.
They do have a real problem with the Pope and with Priest in general as the Bible says that only Jesus can bring a person to God, so they don’t like the idea of having to go through this middle man, its the same problem they have with Confession. They believe in confessing your sins, but think this should either be a public communal confession out loud, or should be directly between you and God, not through a priest.
Baptists celebrate advent, with an advent wreath 4 weeks before Christmas just like we do. They have communion, although it is clearly not the Body of Christ as we believe it, but more of a commemoration.
When you study the two faiths deeply, Catholics believe 99% of what Baptist believe, plus we have additional practices such as a liturgical Mass, written prayers, the idea of patron Saints for different causes, and the entire veneration of the Virgen, etc.
Now, I do agree with the OP, that their idea of salvation OSAS is a little weird. But I have had many discussions on the topic, and I can see why they think so. The idea is that human nature is sinful. None of us are without sin, so that if you think that you must be without sin to go to heaven, no one would get in heaven, except through the mercy of God. So if you believe that Jesus Christ came to earth to die for forgiveness of our sins, then you accept his salvation, and will go to heaven. They believe that salvation is a “free gift” from God, that can not be earned.
They have weird beliefs about earning “jewels in heaven” and different “levels of heaven” depending upon what kind of life you lead. And, they can show you passage and verse that discusses these things. It is the one thing about the Baptists that I summarily disagree with. I believe that salvation is a free gift from God, that can not be earned, but you can reject that gift by committing a sin. Sin is a rejection of God’s grace. The other think I can not live without is the Eucharist, which is why we go to Mass every Sunday although we really have problem with the priests.
Other than that, I have found the Baptists at this church to be truly living a Christian life, and I have grown in my relationship with God through fellowship with them. They are serious thinkers, that discuss and study the Bible, and live a life in pursuit of Christian ideals. I have found that many Catholics I know do not take their faith as seriously, and think that if they go to Mass every Sunday, and confession once per year, then they are good, without really living Christianity day in and day out, and seeking a closer relationship with God.
I suggest going to Baptist Bible study, and then discussing what you learn with your Girlfriend afterwards. Through my discussions with my Baptist friends, I have been able to explain my positions, as have they, and we have both grown closer to God because of it. Through this practice you will be able to determine if the differences are too large to be able to build a family upon.