AP: Today it is so normal for us to designate the four canonical writings, and many other apocryphal ones, with the globalizing term "gospel." It's not immediately clear why we do so. A history without gaps of tradition cannot be constructed with respect to the concept "gospel," neither in the biblical field nor the broader field of Greek linguistics. In the New Testament there is no concept of "gospel" as a book containing the life of Jesus. There is one possible exception and it is very controversial.
This is the beginning of the Gospel of Mark: "The beginning of the gospel of Jesus Christ, the Son of God . . ." It is debated whether this text––which sounds so inappropriate or appealing if one thinks of a writ of diffusion, or propaganda, of faith in Jesus for those who did not know it at all in the Roman Empire––was perhaps an addition, or heading, written by a scribe, in the middle of the second century, when the term "gospel" came to designate a writing that contained the life and teaching of Jesus as the good news. It is clear that only in the second century will this designation of "gospel" appear clearly.
Perhaps the first testimony is that of the "Teaching of the Twelve Apostles" (Didache) 8:2: "Nor do you pray in the manner of the hypocrites, but as the Lord commands in his gospel, so shall you pray." This is followed by the prayer known as the "Lord's Prayer" or the "Our Father." Follows the "Our Father"). The passage of 15:3–5 is also discussed: "Correct one another, not with anger, but with peace, as you have it in the gospel" (perhaps an allusion to a text similar to that found in Matt. 18:15 on brotherly correction).
Others have thought that this phrase should be linked to verse 2 of Mark's writing and understand it: "The beginning (of the book) that explains the message (gospel = good news) of Jesus, namely that the Kingdom of God is near."
Finally, others say that the transition of the word "gospel" as kerigma or proclamation of good news to a book was set by the heretic Marcion around A.D. 145. He must have imagined that when Paul referred to his "gospel"––which he, Marcion, had to restore to its pristine purity––was already thinking of a written text. Therefore, the text he edited as a single gospel––according to Paul's thought, that of Luke, he called it "the gospel." I think this is a suggestive theory . . . and it is quite possible. But it is also possible that this had occurred in the mind of the author of the Didache even earlier.
What does belong to the Old Testament tradition is the general use of the verb "evangelize" (based on the Hebrew Bible, the LXX translation εὐαγγελίζεσθαι, with some passages whose sense is similar to the one of the New Testament). The noun בשׂר is also found in a few cases, although it lacks religious sense (in the Greek Bible: εὐαγγέλιον and εὐαγγέλια) with the broad meaning of "good news," not necessarily sacred, although it is not excluded that it is bad.
In 1 Sam. 4:17 the Hebrew text reads: "The messenger answered, 'Israel has fled before the Philistines. In addition, the army has suffered a great defeat, your two sons have died, and even the ark of God has been captured.'" For the word "messenger" we find the word הַֽמְבַשֵּׂ֜ר (I've copied it exactly from the BHS in case you want to search for it). The root of this noun is "to bring news." Εὐαγγέλιον appears in the Greek Old Testament in only three passages: 2 Kgs. 18:20, 27, and 4 Kgs. 7:9 (as G. Segalla points out in Panoramas del Nuevo Testamento [Estella: 1989], 176-177).
In Deutero-Isaiah (40:9 and 52:7), in the Greek version, the verb "evangelize" appears in the broad meaning of giving the good news, the joyful message of the beginning of the reign of God. Here are the texts: "Go up to a high mountain, joyful messenger (literally "the one who evangelizes") to Zion; he cries with a mighty voice, a cheerful messenger to Jerusalem, cry out without fear. Say to the cities of Judah, 'There is your God.'" "How beautiful are the feet of the messenger (literally "he who evangelizes"), who announces peace, who brings good news, who announces salvation, who says to Zion, 'Your God reigns!'"
And there is another text in the same corpus of prophetic oracles collected under the name of Isaiah, 61:1 that was widely echoed in the New Testament: "The spirit of the Lord Yahweh is upon me, because Yahweh has anointed me. He has sent me to announce (literally "evangelize") the good news to the poor, to bind up broken hearts, to proclaim to the captives the liberation, and to those in prison freedom." Luke uses this text for Jesus in his first appearance in Nazareth: "He came to Nazareth, where he had been raised and, according to his custom, entered in the synagogue on the Sabbath day, and rose to do the reading. They gave him the scroll of the prophet Isaiah and when he unrolled the scroll, he found the passage where it was written: 'The Spirit of the Lord is upon me, because he has anointed me to proclaim the good news to the poor; he has sent me to proclaim release to the captives and sight to the blind, to give freedom to the oppressed and to proclaim a year of the Lord's grace.' Rolling back the scroll, he returned it to the attendant and sat down. In the synagogue all eyes were fixed on him. He began to say to them, "This Scripture which you have just heard has been fulfilled today." And Paul quoted it in Rom. 10:15: "And how shall they preach unless they are sent? As the Scripture says, 'How beautiful are the feet of those who proclaim good news!'"
It has been rightly assumed that the use of Isaiah and the Old Testament background in general has had an influence on the early Christian use of the word "gospel" and "evangelize," although in fact the noun "gospel" as such never appears in the Greek version of the LXX.
Undoubtedly, the background is very similar, but as the use of this word in the Gospels appears in redactional passages, i.e., typical of the writer/evangelist, and therefore secondary (not belonging to the oldest stratum that we can trace back to the Jesus of history, but rather to what the author himself is commenting many years later), it is impossible to assert that from Jesus himself or from his immediate followers was the use of "gospel" directly taken from the prophetic passages of the Old Testament. This is the normal opinion of critics and commentators who are rather skeptical about such matters.