To preach that Jesus is the true King over all kings, the only true Son of God, and therefore the only one worthy of worship is not merely a personal conviction of individual piety but is necessarily a public, political, and polemical proclamation…

It is a kerygma or proclamation. We still use the word in this way today, such as when we speak of “preaching the gospel,” though usually with a sense narrower than the apostles. That is, at least in much of Protestantism “the gospel” has come to refer to the doctrinal information about the justification possible through faith in Christ. Especially in evangelical circles, “the gospel” has come to refer specifically to the forgiveness of sins available through Jesus’s death and resurrection. Although certainly not wrong, this meaning is notably incomplete and narrower than Paul’s own usage, which much more comprehensively refers to Jesus’s entire life, death, life after death, and future return; it is the whole proclaimed message, not just the particular (and partially polemical) issue of “justification by faith,” which Paul has in mind when he speaks of “the gospel.

—  Jonathan T.Pennington,  Reading the Gospels Wisely