Good question. The original "good news" gospel was that which Jesus preached and lived, it was the Gospel of The Kingdom of Heaven that he tried to reach the Jews with, the gospel that they would be preaching today from Jerusalem if they had accepted it. Some of the original foundations and traces of that gospel can be found in the 4 gospels in the Bible. It should be noted that the gospels were written long after Paul's interpretative, post-cross gospel became the norm. To be fair much of it is missing, some of what's left lead to speculations. Jesus has fostered the Christian church as the best exponent of his life's work but the original gospel and the kingdom ideal has yet to be preached and realized.
is this not the Gospel of the kingdom?
Revelation 14:6 (KJV)
6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,
Revelation 14:7 (NKJV)
7 saying with a loud voice, "Fear God and give glory to Him, for the hour of His judgment has come; and worship Him who made heaven and earth, the sea and springs of water."
Revelation 14:8 (NKJV)
8 And another angel followed, saying, "Babylon is fallen, is fallen, that great city, because she has made all nations drink of the wine of the wrath of her fornication."
Revelation 14:9-10 (NKJV)
9 Then a third angel followed them, saying with a loud voice, "If anyone worships the beast and his image, and receives
his mark on his forehead or on his hand,
10 he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb.
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Revelation 14:13 (NKJV)
13 Then I heard a voice from heaven saying to me, "Write: 'Blessed
are the dead who die in the Lord from now on.' " "Yes," says the Spirit, "that they may rest from their labors, and their works follow them."
Revelation 14:14 (NKJV)
14 Then I looked, and behold, a white cloud, and on the cloud sat
One like the Son of Man, having on His head a golden crown, and in His hand a sharp sickle.
Revelation 14:15 (NKJV)
15 And another angel came out of the temple, crying with a loud voice to Him who sat on the cloud, "Thrust in Your sickle and reap, for the time has come for You to reap, for the harvest of the earth is ripe."