I have tremendous respect for everyone here in all of these forums, for there are far more learned and mature Christians than I here. In every forum, there they are, and I defer to them.
Not everyone, though, by the grace of God, was exposed to as much Roman Catholicism as I was. Taught by a semi-cloistered order of nuns for 12 years, and through grad school courses by Jesuits in college; I took grad courses in Catholic liturgy and Catholic moral theology. I knew they were wrong, but I didn't know HOW wrong. I knew they were idolatrous, but it hasn't been until the last few years that the Lord has given me some sense of exactly what was/is going on in that organization that, worldwide, has one billion adherents.
If there's one thing I've learned in all my years of born-again, fervent belief in the doctrines of grace - and with over 90% of my dear, extended family and friends still firmly rooted in the RCC - it's that you cannot successfully witness to a happy Catholic.
Only the Holy Spirit can bring someone out of the RCC. There is absolutely nothing that we can do or say by our words, our witness, our "friendship evangelism," or anything else that can possibly interest a real Catholic in the real Gospel, not even slightly. They're
so convinced of "works salvation" -- and even I am still picking off those "works burrs..."

When you attend a mass, you give assent to it in subtle ways, whether you think that's what you're doing or not. You give the impression that "real Christians" have no objection to standing shoulder to shoulder with Catholics at their masses, so there must be no problem with them. Believe me, they're hoping and praying that
you'll come back there
for real the next time and that you'll even join one of their "Rite of Christian Initiation for Adults" (convert) classes. The vast, vast majority of adult "cradle Catholics" give no thought to their ever leaving, not if the Holy Spirit has not begun His work in them.
If you attend a mass, ask yourself whether you would want the Lord Jesus Christ walking alongside you as you walk into that church and look at the statues, the light on the altar that's supposed to signify the presence of the "Blessed Sacrament," the Stations of the Cross on both sides of the church and "the side altars" (which Catholic churches are still supposed to have). The altar on the left is "the Mary altar" and the one on the right is "the Joseph altar." There are so many other things... The tract racks with little prayers to St. Jude (the patron saint of hopeless situations), St. Anthony (the patron saint of lost items), the formulae for novenas to Mary, the prayers to St. Joseph, etc., etc.
But first, before you enter that church, read Hebrews 7 through 10...
I'm old enough to remember the mass said in Latin... How many masses have I attended in my lifetime?
Thousands... I went to mass two to three times a week from first grade through 12th, and once a week during college and thereafter, until I finally couldn't take any more. But I praise the Lord! He brought me out - and it's all covered over by the Blood. "Hoc est corpus meum" ("this is My Body") said the priest in Latin. In my old church, if someone dropped a host on the floor of the church, it could only be retrieved by the "consecrated fingers" of a priest, and the spot where it had landed would have to be covered by a "blessed linen" until "holy water" was used to make that spot okay for people to walk on again. Idolatry?
Oh, yes!
Please, if you still doubt what I've said above, go to Richard Bennett's website,
Berean Beacon and read... He's a former Catholic priest who now devotes his life to bringing others of the elect who remain in the RCC out... Or read the book, "Far From Rome, Near to God." Or go to Mike Gendron's "Proclaiming the Gospel" web site (I don't recommend that one as much for Reformed Protestants as others, but it's still worthwhile). Or try to find the book "Night Journey from Rome to the New Jerusalem" by Clark Butterfield, another Catholic priest who left, underwent conversion, began to preach the real Gospel - and then died under somewhat mysterious circumstances.
As I said on the now-closed thread, I don't question other people's consciences or their status as Reformed believers or Christians just because they find that they can go to Catholic masses or other events. The Lord gave me a different life history, and part of that means that I can't do it - but I've
no quarrel with others who can. I just want others to have "informed consent" when the occasion arises for them to attend a Catholic event...
May the Lord bless this important discussion to His glory and for His always perfect purposes!
Margaret