The qualifications to enter the Body of Christ are not the same as the qualifications to enter the kingdom.
That is just one of the errors promoted by those within the Neo-MAD movement. Here we can see that both Jews and Gentiles are baptized into the Body of Christ:
"For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ. For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit" (1 Cor.12:13).
In this passage Paul uses the pronoun "we" twice and from his introduction in that same epistle we can know that that pronoun is not only referring to those in the church at Corinth but also "all that in every place call upon the name of Jesus Christ our Lord":
"Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints, with all that in every place call upon the name of Jesus Christ our Lord, both their's and our's" (1 Cor.1:2).
All of the Jewish believers living in the first century did indeed call on the name of Jesus Christ so therefore all of them belonged to the Body of Christ.