I disagree with the posts in here, but I won't waste my time getting into what will inevitably be a fruitless argument (hard to dissuade people from what they've been taught for years, no offense).
But anyway, we are under the assumption that the gospel only includes the death, burial and resurrection of Messiah.
Don't get me wrong, that is the key element, but it is not true understanding of what it is. Consider these passages:
Galatians 3:8 And the Scripture foreseeing that YHWH would justify the nations by faith, preached the gospel before to Abraham: "All the nations will be blessed in you."
Say what? The gospel was preached to Abraham when Yahweh said "in you shall nations of the earth be blessed"???
Hebrews 4:2 For, indeed, we have had the gospel preached to us, even as they also; but the Word did not profit those hearing it, not having been mixed with faith in the ones who heard.
If we look a few verses before this in the previous chapter (3:17), we see that those in the wilderness (Israel when they were brought out of Egypt) qualifies the "they also" here in this verse above.
The gospel was preached to Israel?
Luke 4:17 And the scroll of Isaiah the prophet was handed to Him. And unrolling the book, He found the place where it was written:
Luke 4:18 "The Spirit of YHWH is upon Me. Because of this He anointed Me to proclaim the gospel to the poor; He has sent Me" to heal the brokenhearted, "to proclaim remission to captives, and to the blind to see again," to send away the ones being crushed, in remission,
Luke 4:19 "to preach an acceptable year of YHWH."
Here Messiah quotes the LXX (or the Hebrew that the LXX was translated from) about preaching the gospel (he's reading what we would call Isaiah "61:1-2") What is he going around preaching?
That he died and rose again the third day for sins?
No. He makes it clear. A clear understanding of the prophets and the whole theme of scripture will reveal to us what the gospel is and how Messiah is the major part in it. All throughout the prophets is mention of a Savior and Redeemer and Deliverer of Israel known as the Messiah. He was supposed to restore Israel and unite both divided houses and deliverer the "captives/exiles". Check Isaiah 11:11-13, Isaiah 49:5-6, Ezekiel 37:16-28, and Hosea 1:11 for a few references.
The gospel is the restoration of Israel (also see Acts 1:6-8) and the deliverance of Israel's (mostly divorced Ephraim Israel; see Jeremiah 3:8 and Ezekiel 22:15 for a couple references) seed scattered and held prisoner throughout the nations and in the fulness of the nations (Genesis 48:19; Romans 11:25).
Messiah said he came for the lost sheep of Israel alone (Matthew 15:24).
By biblical, prophetic definition, if Yahshua did not come to deliver Israel and regather her exiles, then undoubtedly he is not the Messiah.
How does this tie in with the scripture about Abraham being preached the gospel, for example, and the rest of the New Testament? Abraham's promised seed (Israel) was going to be mixed and blessed with the rest of the nations, him becoming "father of many nations" with Israelite seed filling the globe (though you may not know it, there is possibly about 3-4 billion Israelites in the world that all look and act like pagan gentiles...amd you just may be and probably are one of them; but it doesn't matter, of course, if you are not redeemed through Messiah or know his true teaching and message).
In the hint understanding however, the "seed" of Abraham is also Messiah (as revealed by Paul in Galatians 3:16), and because of Messiah, the world being filled with Israelites (the "gentiles" of the New Testament; this can be proven if asked) received atonement by his blood. Divorced Israel had to be forgiven. The New Covenant to reconcile both houses of Israel (Jeremiah 31:31) has to be sealed in blood, as with the first one made at the foot of Sinai.
Messiah's blood alone could have accomplished this. For what reason? Because Yahweh had to become man so he could die to make the old covenant of no effect (not the contents) because he was the author of the Old Covenant (check Hebrews 9:16) and because Israel had fault, and also because according to Yahweh's own Torah, a man cannot remarry a wife that he divorced if she becomes defiled (like Israel did; check Jeremiah 3:1 and Deuteronomy 24:1-4 for insights concerning a man divorcing his wife and how it relates to Yahweh). Israel was Yahweh's wife. The only way to release Israel from the law of a husband (spoken of by Paul in Romans 7:1-4) was to have the husband die (which he did in the person and flesh of Yahshua).
Yahweh wanted Israel back (see the divorce also in Hosea 2:1-2 and the prophesied redemption and return in Hosea 2:16-20), and by Messiah's own declaration that a man cannot divorce a wife in order to marry another (Matthew 5:32), we know that Israel remains Yahweh's people and bride in his heart, and that he did not marry gentiles.
What's going on in the New Testament is the regathering of gentiles (who are, according to the scripture, Israelte exiles living as gentiles, although this is a mystery revealed only by revelation, but it can be proven and seen with overwhelming evidence in the New Testament) by the ministry of the apostles, including Paul.
Paul was not searching for pagans and non-Jews and non-Israelites. He was an apostle to the nations (not to the pagans in the nations) to find and preach and proclaim liberty (from exile, not from Torah) to the scattered seed of Israel by the grace given to them by the atonement of Messiah, allowing them to return to the sheep fold (Paul's letters, such as Galations were against certain heretic Jews and other false masters that tried to enslave Ephraim and deny them their liberty by using them as boast tools, such as is found in Galatians 6:13, and to treat them as unequal salvation heirs in Israel by saying they were still unclean and not saved or justified until they had kept Torah along with their own human dogma; Paul was not preaching against Torah in Galatians, or Colossians or Romans or Corinthians or any letter for that matter). This is the reason for Messiah's death. He did not give grace to oppose Torah or as opposed to Torah (as many teach). He gave it for the reasons above, according to scripture.
I am not saying true pagans cannot be saved. Far from it. Just the opposite. Messiah was also given for a "light/beacon" to the non-Israelite nations (Isaiah 49:6), but that call is for them to join Israel. In the return of Ephraim Israel, all the rest of the world is called to salvation and blessings as Israel, justified and redeemed from all past deeds as sinners and pagans.
This is the gospel. The restoration of both houses of Israel and the kingdom of Israel under David, the King (which is why it is also called the "gospel of the kingdom").
Teaching the gospel to all nations as Messiah commanded is not to go looking for pagan sinners of different religions (many evangelist are in error going to pagan countries and places specifically looking for those who are pagans so as to convert them to Christianity). It is to go out into the nations and find scattered Israel in Israelite nations and in all other nations, at the same time, calling whoever hears the gospel by the light shown by redeemed, Torah-honoring Israelite men. The gospel preached today is nothing but a "my religion is better than yours, so believe in Jesus or go to hell" message by many evangelist and those who call themselves "prophets" and "pastors".
Why would Messiah tell his disciples to go preach to pagans who would have no knowledge of Messiah and wouldn't care about Hebrew prophecy concerning atonement? Foolish. "Jesus died for your sins" means nothing to a Hindu or some other pagan. And how some of these false, self-proclaimed evangelists "win souls" is by threatening them with hell, or promising them the usual stuff taught in the pulpit (joy, peace, a job, money, miracles, or bribing them with food and money and other nonsense taken out of context that has nothing to do with the bible).
Anyway, aw man, I could continue forever. I could write a book, I suppose (lol), but I'll leave whoever reads this with this little insight. Be open-minded. Pray to Yahweh for truth. We all should.
But anyway, 1 Corinthians 15:1-5 is still true. It's just that there is more to it. Also, his resurrection is important by reason for our hope in resurrection, as Paul also states here. It is also, I believe, the sign of the New Covenant. Every covenant has a sign. Abraham's was circumcision, the one with Noah and all flesh was the bow, the one for the covenant at Sinai was the sabbath, etc...
The sign for the New Covenant in Messiah's blood is his resurrection.