What is included in the kerygma?

I make a distinction among the kerygma of Christianity, the apostles' illuminations and applications of it and teachings of lesser import: core Christian doctrine from Jesus and the apostles as opposed to denominational opinions on various tangential matters. Perhaps I should say something about the content and limits of the kerygma. As I use the term, the kerygma consists of the things Christ taught the apostles, by word and deed--which they then proclaimed. As it turns out, this includes not only the sayings and parables and commandments we all think of, but also the messianic prophecies of the Old Testament.  

...beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself.  (Luke 24:27)

I find it a little disappointing that the Bible does not provide a list of those passages. But at the time of writing, giving a list would not have been necessary. The apostles, to whom Christ is here speaking, were Jews who believed the messiah would come, and followed him when he did.  Much of the early church was of that sort: knew a messianic prophecy when they saw one. Given the key idea, that these referred to Jesus' life, they could work out the matter from there.

When preaching to Jews, the apostles made use of Old Testament prophetic material. Peter's sermon at Pentecost (Acts ch. 2) quotes the prophet Joel and King David. Preaching at Solomon's Porch (Acts ch. 3) he refers to "all the prophets" as foretelling the Messiah's suffering and the redemption of the saved, and quotes a particularly relevant passage from Moses.

That was no doubt an effective tactic to use when preaching to people who knew and believed the Hebrew scriptures. In Acts 17 we see that when Paul preached to the Jews at Thessalonica, "he reasoned with them from the Scriptures, explaining and proving that the Messiah had to suffer and rise from the dead. 'This Jesus I am proclaiming to you is the Messiah,' he said." But when Paul found himself preaching before the Greek philosophers of Athens, he sailed a different tack. He cited a couple of Greek poets in the process of giving a broad outline of the plan of salvation. There would have been little point in quoting prophets his audience had, likely, never heard of.

It was fortunate, likely providential, that Paul just happened to be knowledgeable in Greek poetry. The outline of what he said, though, accorded with the Old Testament scriptures and the Christian gospel. Though he does not quote a single prophet or cite any book of the Bible, what he said had its bedrock in the Hebrew prophets.

The heart of the gospel has been spoken by those prophets from the beginning. The relevance of this to my resolve to speak only the kerygmatic message before the unsaved is fairly obvious: I ought not draw too restrictive a definition of the kerygma, saying for example that it is only the words of Jesus. It is those, and it also includes by reference the prophets who spoke of the coming Messiah, for Jesus incorporated the prophets in his teaching. The apostles clearly got the idea, making effective use of the prophets in their evangelizing, where possible.

However. . . Christians these days have scant opportunity to evangelize Jews who are, at the same time, knowledgeable in their own scriptures and open to considering the idea that Jesus could be the Messiah. Most people we deal with are Gentiles and have never read the Bible. If we make a habit relying on Isaiah, or Jeremiah, or another prophet, such hearers will have no idea what we are talking about.

Paul, who adjusted his sermon when preaching to gentiles in Athens, later found himself in Corinth, again preaching to pagan Greeks. There he resolved to talk initially about nothing but Christ and him crucified (1 Corinthians ch. 2), which I take to be the best plan, under most circumstances, in our own times.