The other night, we had some of our friends over and I was discussing the history of the Church. He is very interested in apologetics and learning how to defend and explain his faith (which is, by the way, a wonderful goal for all people of faith, not to mention all Catholics). Many times in our discussion, he would mention that the non-denominational Christians he had been speaking with would deny that Church traditions went back as far as they claim to go. Things such as the Trinitarian baptism, relics, saints, etc. As we talked, it occurred to me that Catholics have a resource which is seldom called upon to defend the truth of the Catholic Church: the Didache.
For those who have not heard of it before, the Didache (also known as the Teachings of the Twelve Apostles) is an ancient text which claims to be the summation of what the Apostles taught. It is estimated to have been written between 50 and 110 AD. It is mentioned by many of the Church Fathers before the Bible was compiled and just narrowly missed inclusion. It was lost for many centuries and was only rediscovered in 1875.
This is an enormous help for the Church, because it is a documented piece of evidence that shows a very Catholic view of the early Christian world. I also disrupts the theory that Catholics simply made up core pieces of the faith.
To give an analogy, imagine for a moment that you go to a barbecue. You've been to many places that serve BBQ, but this place has something different. The chefs have a very specific way that they do theirs and they only smile and politely refuse if anyone suggests changing it. When pressed, they tell you that their recipie is unchanged from the very first one, handed down by the greatest BBQ master of them all.
Of course, most people would scoff at such a claim. "That can't be true. You're getting a bit conceited about your own tradition. There's no way that you have the original BBQ recipie."
Then, one day, a historian runs across an ancient document (say, 1000 years old) which mentions barbecue and lists a recipie. When compared with the one being used by that one group of chefs, it is found to be a match. All of the key ingredients are there, done in the same order, in the same amounts. Other barbecue recipies may be similar, but no others have the same integrity.
If such a situation were to happen, the claims of that group of chefs would be greatly bolstered. Their statement doesn't seem so far-fetched anymore.
This is similar to what one finds when reading through the Didache. It supports Catholic tradition and practices. It is nearly free from the claims of corruption, because it was considered lost for a great deal of history. Christians who dislike the Catholic Church are stuck too, because it predates the Nicene creed and the accepted doctrines of the Trinity. It may even be older than some of the New Testament. It is widely known and accepted by the early fathers of the Church, which throws out claims that it is a heretical work. In short, the existence of this document lends credibility to the Church's statement that its teaching remains unchanged (indeed, unchangeable) from the very earliest days of Christianity.
On a broader level, it gives another area of consideration. If one can see and acknowledge that the Didache lends credibility to the Church's claim that she has the original teachings of the Apostles, why should she not be trusted when making other claims?