So, the principal diiference  of membership, was that Paul’s followers are on an equal level with him, just  believers with no physical sign,  whereas the followers that were not jews were proselytes and subjected to being circumcised as proof.  So, their “proof” was physical and  Paul’s was spiritual.

 The followers of  the original apostles  also were led to believe that  Jesus’ crucifixion  meant that  they were pardoned of their sins, but that they must do “good” in order to be worthy of being blessed. 

 Paul stressed that there is nothing that could be done that would change anything.  Nothing could be greater than the sacrifice God's son had made for mankind,   and through God’s grace they understood  that their sins were justified..wiped clean.

 I don’t know if Peter preached of good and evil and what might be their final destination at death,  nor whether or not he believed that all mankind  would be saved,  but Paul made it very clear that  ALL would be saved.

 Peter’s followers  were taught that  they would  rule together with  Jesus on His return here on earth, as the “chosen” people,  with  each of the 12 tribes receiving apportioned shares.

 Paul’s followers would rule, together with  the Christ, in the heavens.

As believers,  you recognize the difference in what we know to be true compared to  those who attend  traditional churches .   A carryover,somewhat, from the differences of long ago,  notably that they don’t realize that  their sins are justified and they still insist on “doing” something to be worthy of God’s blessing.  Nor do they believe,  that through the grace of God, ALL will be saved.  They still believe in the "carrot and the stick",  do “good” and go to “heaven”do “bad” and go to “hell”..paulnbob