What obligation did Gentile believers have toward the Jews because they shared in Israel's spiritual things?

Les teaches that in Romans 15:25-27, Paul went to Jerusalem not to preach, since he had no ministry among the Jews there, but to bring financial help to the saints—the poor believers in Jerusalem. The churches of Macedonia and Achaia had been pleased to make a contribution for them, and Paul says their debtors they are: if the Gentiles were made partakers of Israel's spiritual things, then the duty of the Gentile is to minister to the Jew in carnal or material things. That was the responsibility. As yet Israel had not been totally set aside: the Temple was still going and Israel was still in the land, yet these Jewish believers were destitute and had no welfare system. The Temple priesthood would not take care of them because they had embraced Jesus of Nazareth, whom the religious leaders detested, so they were in an island of need. Their only hope was the collection from the Gentile believers sent to Jerusalem. Les also notes that Macedonia was northern Greece and Achaia southern Greece, and these people were poor themselves, eking out a living in a rough, mountainous countryside.