Belief in Jesus makes the two groups one.
Ephesians 2:14 For he himself is our peace, who has made the two groups one and has destroyed the barrier, the dividing wall of hostility,
That was done on the cross:
Ephesians 2:15 by abolishing in His flesh the law of commandments and decrees. He did this to create in Himself one new man out of the two, thus making peace
Ephesians 2:17 He came and preached peace to you who were far away and peace to those who were near.
The Gentiles were those who were far away.
Colossians 1:20 and through Him to reconcile to Himself all things, whether things on earth or things in heaven, by making peace through the blood of His cross.
Colossians 3:11 Here there is no Greek or Jew, circumcised or uncircumcised, barbarian, Scythian, slave, or free, but Christ is all and is in all.
Just because not all understood exactly, when Jesus died, that does NOT mean there is another gospel.
When Jesus died on the cross, he went to prison/hell, and preach the gospel to those who died in the times of the flood---there wasn't even Jew and Gentile yet---but they were still given the one and only gospel that saves.
Then Jesus ascended to the highest place---that is about future people who will be born.
There is only one gospel that saves anyone.
There were those who disobeyed and died before Jesus came to earth, though they were dead their spirits went to a prison, unlike the spirits of the righteous. After Jesus was crucified, he preached to those who were dead, he preached to the spirits in prison, the spirits of those who had died and disobeyed long ago (see 1 Peter 3:18-19). Those people who disobeyed and died before learning of Jesus...Jesus preached the gospel to them, so that they might be judged according to men in regard to the body, but live according to God in regard to the spirit (1 Peter 4:5-6). For Christ died for sins once for all, the righteous for the unrighteous, to bring us to God, even those who lived and died before Jesus.
You see, Jesus came to earth and taught those on earth. Then Jesus descended to the spirits in prison to preach to them, to those who disobeyed long ago. Jesus then ascended higher than all the heavens. Jesus filled the whole universe (see Ephesians 4:10).
These scriptures show we have living, thinking spirits that live on after the death of the body. Some spirits go with those who disobey, and spirits of the righteous live in heaven. These scriptures show that our spirits live on, and how Jesus filled the whole universe.
One gospel that saves, for everyone, ever.