Christ preached "The Kingdom Message" to the lost sheep of the House of Israel, as did Peter and the rest. When Paul came along he was made "The Apostle to the Gentiles", and he preached "The Grace Gospel" to the Gentiles. That's a simple truth. Most of you cannot seem to comprehend it.
Today, only "The Grace Gospel" is in effect for both the Jews and the Gentiles.
the Gospel is inside the offer to Israel about the kingdom, which did come and was not a Judaistic theocracy. The term is actually 'reign.' Christ was about to be enthroned, and was, as found in Ps 2, at the resurrection, which also took place because of his redemptive sacrifice.
You are imposing 2P2P on the NT which is not there at all. It is actually a unified message, as found through all the letters etc.
To repeat, here are some reasons we know the redemptive Gospel of Christ was being preached already:
1, they knew Christ was the 'Lamb' of God. Hard to miss the significance of that title in that decade!
2, they knew very soon that Christ had and proved the authority to forgive sins
3, they knew that the 'cross' they were going to take up was the preaching of his cross in the well-known 'if any many would follow me, he must...' verses
4, they knew the dynamic of grace was in operation very early because the disreputable women episodes were about how 'those forgiven much love much' vs the Pharisee mentality.
5, they knew fairly soon that Christ referred to his upcoming event as an 'exodus'--that would be a new one, just as everything else in Judaism was being rendered new.
These are all simple truths that you GM cannot seem to comprehend.
There is no indication at all of a theocratic, Judaistic, temple- or Jerusalem-based kingdom. That is a misguided belief the masses grew up with and tried to impose on him, which he refused, as in Jn 5 and 12:34.
Those who do become missionaries of his Gospel (see the middle of Rom 10) do go on to 'reign in life' and to be 'more than conquerors' as Romans says, but very few from Israel believed.