Catholics have a vastly different vocabulary than Protestants. Words common to us both are understood very differently. Catholicism goes back to the culture and understanding of the first century and is born of Judaism. The way we understand religious words is tied to the past, not todays individualistic, post-enlightement thought.
For example "grace." When I was a Protestant the word wasn't defined as anything other than a good feeling, a type of forgiveness and high-five from God. Catholics see it as the actual power received from heaven to overcome. Grace for a Protestant is more symbolic, for Catholics it is real.
I have found this to be true about so many of Catholic and Protestant differences. Catholics see as real what Protestants see as symbolic-- Peter given the keys to bind and loose; a religious, organized, structured (or visible) church; "take eat this is my body"; "be fruitful and multiply" and on and on.
Catholics do not reject scripture, they just interpret it differently. They see the ways the Father's of the church interpreted scripture in the first few centuries of Christianity more trustworthy than most of those today. We look back to get our answers; Protestants look at today.
We love rituals! We think it is God's love language (after all look at the Old Testament! Look at Jesus at the last supper, His command for baptism and the imagery of prophecies. All very ritualistic.)
We think differently on the very basics. Catholics have throughout the centuries--believed that man must be taught. We must go out and search for wisdom, pursue her and work for her. Wisdom and understanding doesn't flower up within us naturally, it is cultivated by hard work. Protestants tend towards believing that everything should be simple and the Holy Spirit plants in our hearts everything we need to know. (They, of course, also use the Bible.) But their mindset is that we develop spiritually from within and flow out. The individual comes to church to give knowledge and truth to the group, whereas, Catholics go to church to receive knowledge and truth given to the church as a whole.
Protestants see each individual as the final judge of truth, they only trust themselves and their conscience. Catholics teach that the conscience must be cultivated and trained by the church and you can trust God's appointed church to judge truth. It is an individualistic versus community idea. And we see this as firmly rooted in what Christ taught through the Apostles and written in God's Holy Word.
Again.... I am having whole conversations in my head with my family and friends... I doubt they would listen to any of it. So I have them here--or at least make notes of all the conversations I would have if I could.
It took me six years of intensive study (dozens of books, talks--or better said--arguments with priests, listening to online sermons and debates) to "get" Catholicism, so I know I won't be able to do much to open up understanding in a sound bite.
There is a song from a musical with the words, "If they could see you through my eyes, they wouldn't wonder at all. If they could see you through my eyes, I guarantee they would fall.... like I did!" That is how I feel about Catholicism. The doctrines show me a Jesus I never expected. Scary. Powerful. Dominating. Authoritative. Strong enough to carry me when I am weak. Strong enough to heal the sins I fall so easily into. Strong enough to give me supernatural courage to face life and the spiritual battles of each day. Strong enough to make me a saint. Strong enough to make me obey.
And when you encounter that kind of strength, there before you each time you gaze at a crucifix, you see that He is strong enough to save. Strong enough to have mercy. Strong enough to love.