What are good scripture passages to get my protestant friends wheels turning?

I am looking for passages of scripture like Mt. 16:18, John 6, 1 Tim. 3:15 that seem to get my protestant friends wheels turning. My friend is very versed in the Bible and I want to present him with a few passages to study that point to the Catholic church. I know that many exist and just thought you all might have some good areas to start the first of many conversations.

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