Recently I began reading "The Effective Invitation: A Practical Guide For The Pastor" by R. Alan Streett, chairman and professor of Evangelism at The Criswell College and editor of the Criswell Theological Review. Chapter 1, "Tell Me, What Is The Gospel," deals with the theological content of the Gospel message. I will briefly summerize the chapter's contents.
Streett cautions against making an appeal to others to accept Christ as Lord and Savior when a clear proclamation of the message of the Gospel has not been preached. There are two parts to the Gospel message, proclamation and invitation. Proclamation must always precede an invitation to listeners to respond to its truth. Three New Testament words deal with proclamation: kerygma, kerysso and keryx. Kerygma, appearing 8 times in the New Testament, refers to the content of the Gospel. It is translated in English translations as "preaching" (ex. 1Cor. 1:21). Kerysso, appearing 61 times, means "to proclaim" or "to preach"; it refers to the act of preaching. Keryx, appearing 3 times, refers to the preacher. Paul used the word twice to describe himself (1Tim 2:7, 2Tim 1:11). The word also includes the concept of an ambassador in its meaning. (1Cor. 1:17, Eph. 6:19-20, 2Cor 5:20) The preacher does not proclaim merely for the sake of doing so. An inseperable component of his motivation is an expectation of response. Three New Testament words deal with evangelism: evangelion, evangelizo and evangelistes. Evangelion, appearing 77 times, simply means good news and is a synonym for kerygma (Rom 16:25). Evangelizo, appearing 55 times, means to bring or announce glad tidings. Evangelistes, appearing 3 times, meaning bringer of good tidings, is translated as "evangelist" and is a synonym for keryx.