You avoided my question. Why were the disciples told to only preach, "the kingdom of heaven is at hand", only to Jews and not the Samaritans or Gentiles? Why were there exclusions if it was for the whole world? Btw, no mention was ever given in this message of the death, burial, and resurrection for sin. This is what Paul's gospel was all about.
Jesus was preparing them for what was to come. Once Christ had prepared the disciples he sent them out to complete what he started, He dwelt among us and now the Spirit dwells in us:
And Jesus came and said to them, “All authority in heaven and on earth has been given to me. 19 Go therefore and k make disciples of all nations, baptizing them m in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them o to observe all that I have commanded you. And behold, I am with you always, to the end of the age.” (Matt 28:18-20).
We see the disciples carrying out their commisssion to carry on the work of the kingdom that Jesus set them:
"But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.”" (Acts 1:8)
As Paul says, the good news is the power of God for salvation to everyone who believes... To the Jew first (Rim 1:16). And Paul and his coworkers themselves carried on that work of the kingdom of God. Paul and his coworkers carried on that work of the kingdom of God along with all the apostles, disciples etc.
So the good news or gospel paul believed and taught is the work of the Kingdom of God.. Preaching and teaching the word etc.
Regarding samaritans, theres a whole chapter in John, where many Samaritans were saved, when Jesus stayed in their town, for two days and they believed His 'word'.
Many Samaritans w from that town believed in him because of the woman's testimony, “He told me all that I ever did.” 40So when the Samaritans came to him, they asked him to stay with them, and he stayed there two days. 41And many more believed because of his word.
What was Jesus word, well quite simply. He being God (in the incarnation) took on flesh, he was as Paul says 'the Pascal lamb', who takes away the sin of the world as john tells us. He fulfilled the law, he prevailed were man failed. Because he so loves the world, he gave himself, to die on the cross, so that whoever would believe in him will have eternal life... Its all in the gospels, and Paul draws this out for us in how to apply this to our lives, as his letters deal with problems within the churches he planted.