Q. My question is this: Are Catholics saved, even if they continue in “worship” of Mary and other saints?
A. In Isaiah 42:8, God said, “I am the Lord; that is my name! I will not give my glory to another or my praise to idols.” It’s a combination of the first two commandments, “you shall have no other gods before Me” (Exodus 20:3) and “you shall not make an idol in the form of anything in heaven or on earth … you shall not bow down to them or worship them” (Exodus 20:4). These are the standards. If a Catholic gives the glory only God deserves to Mary or a Catholic saint, or bows down before a statue of one of them to pray or give thanks to them, it would be a violation of the first and second commandments.
Repeated willful violations of any commandment would cause an observer to question a person’s spiritual condition, and I imagine there are many Catholics around the world who are guilty of idol worship. But I would not go so far as to say that no practicing Catholic can be saved. That’s a judgment only the Lord can make, because only He knows the motives of a person’s heart.