I have already quoted Galatians 2 here before. James agreed to confine his ministry to the Jews only, and Paul was given the right to minister to all Gentiles. Both have their respective gospels, as stated in verse 7. Galatians is the gospel of the Gentiles.
7 But contrariwise, when they saw that
the gospel of the uncircumcision was committed unto me, as
the gospel of the circumcision was unto Peter;
8 (For he that wrought effectually in
Peter to the apostleship of the circumcision, the same was mighty in me toward the Gentiles
9 And when
James, Cephas, and John, who seemed to be pillars, perceived the grace that was given unto me, they gave to me and Barnabas the right hands of fellowship; that we should go unto the heathen, and
they unto the circumcision.
In the Gospel of the Kingdom, which is for the circumcised Jews, there is no need for them to believe that Jesus died for their sins and rose again as a sign that they are now justified in the eyes of God.
All they need to do is to acknowledge that Jesus is the promised Messiah and King sent to them. As the Gospel of John concluded in ch 20,
remember he was one of the 3 apostles who agreed to confine their ministry to only the Jews,
29 Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.
30 And many other signs truly did Jesus in the presence of his disciples, which are not written in this book:
31 But these are written, that
ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.