I favor the approach given by DebChris and Yeoman as it relates to church history. Based on many debates with Protestants I’ve developed a process (meant to be a dialogue) that is easy to remember and can be applied to nearly every situation where you are questioned:
Step 1: Jesus said He would build His Church and protect it (MT 16:18)…[That’s the Church I want to be a part of so who/where is that Church today?]
Step 2: Distinguish between today’s Church and that of the first 800 years…[Today, there are multiple Christian denominations all claiming that they are “that Church” and teach the truth including your neighbor’s. But, who’s right? Who’s got the real truth and not something man-made? In the first 800 years there wasn’t this problem because there was just one single universal Christian Church. No other groups even claimed to be “that Church” that Jesus built. Remind her that there weren’t denominations as we know it today…there was just one.]
Step 3: Since there was just one Church in the first 800 years either that Church taught the truth or Jesus failed to keep His promise to protect His Church…[This step is really important and you’ll have to get your neighbor to think hard about this. Since we know that Jesus can’t fail we then know that this single Christian Church MUST have taught the truth. The only other option I’ve heard Protestants give is that the real Church was hidden for 1500 years. At this point you know they’re in panic mode.] [so what did the early Church believe?]
Step 4: The Church of the first 800 years believed in the Eucharist, infant baptism, Mary as Mother of God and ever-virgin, a 73 book Bible, praying for the dead, and no salvation outside the Church amongst other beliefs…[We know this through the encyclicals as written as a result of each Church Council. In the first 800 years there were 7 such ecumenical councils and the beliefs of the Church are documented for all to see. The first 2 councils were held before even the books of the New Testament were formally agreed upon!]
Step 5: The beliefs of the early Church, which we know taught the truth, are the beliefs of today’s Catholic Church. Hence, we know the Catholic Church is the Church Jesus built as it is the only one that has faithfully preserved the beliefs of Jesus’ early Church. [All other Christian belief systems have strayed from the truth of the early Church beliefs in some way causing them to be fraudulent]
The only reason I’ve stopped using quotes from the early Church Fathers is because there are some questionable quotes from them where they use the word “symbol” as it relates to the Eucharist and a good Protestant debater will use them. The encyclicals are based on the entire magisterium rather than individual church fathers and is a better indication of what the Church actually believed…and there isn’t anything left for interpretation.
Every Protestant will question our beliefs with their interpretation of scripture passages as “proof” that we’re wrong. I say, “although I can appreciate where you’re coming from and your interpretations are plausible, they’re just not what the early Church believed and I choose their interpretation over yours as it allows me to prove that Jesus kept His promise to protect His Church.”
I hope this helps.