Over at Tough Questions Answered, I noticed that they posted this graphic of the Trinity:

This image is pretty good at conveying who is who and what is what. But you may be asking yourself: how the heck did those Christians come up with that doctrine? Did God come down and tell them that? Well, anything I say is probably going to be wrong or heretical, so let me just pass you over to Greg Koukl of Stand to Reason and you can get an accurate answer to that question.

Here is an excerpt that explains what he is trying to do in his answer:

The particular question that came up was that my view, or the Christian view, of the Trinity is inconsistent with the Scripture. That was the objection. That’s why John 20 was raised as a verse and a number of other verses were raised as contradicting the orthodox notion of the Trinity. In fact, it was questioned as whether such a thing could be an orthodox notion because Jesus Himself didn’t teach it.

Now it’s clear that Jesus did not teach the Trinity as I would teach the Trinity because it’s synthetic in that it’s taking a number of different things and synthesizing them into a doctrine. But the synthesis is legitimate if each of those things is actually taught in the Scripture.

Remember, he is answering this question from a Christian perspective, so he is allowed to use the Bible, since Christians believe that it is at least a generally reliable record of Jesus’ public ministry. This is the best short answer I’ve seen so far, from a first-class apologetics guru.

One criticism. Before I cite Bible verses in a debate, I always explain the rules that determine whether a verse is admissable. (I explained the rules as they apply to the resurrection here). But Greg just cites the Bible as if it were inerrant. That would work on me, but it might not work on my atheist co-workers. A better way is to use only the verses that are early, multiply attested, and pass the other standard historical criteria.