Why did the churches in Macedonia and Achaia make a contribution for the poor among the saints in Jerusalem?

Paul himself had organized for the collection of an offering to the church in Jerusalem from the churches instituted by him, and the purpose thereof was precisely to teach them what their position towards Israel ought to be: For Macedonia and Achaia have been pleased to make some contribution for the poor among the saints at Jerusalem. For they were pleased to do it, and indeed they owe it to them. For if the Gentiles have come to share in their spiritual blessings, they ought also to be of service to them in material blessings (Romans 15:26–27).

Even though a partial hardening had come over Israel at the time, there was also a believing, Messianic Israel present in Jerusalem. The Gentiles are being incorporated into this Israel, and the new branches acknowledge the old root by sending money to the poor among the saints of Christ in Israel. Apparently, there was great poverty in the Jewish Christian church in Jerusalem. It is not the extent of the need itself that motivates the Gentile Christian churches, however, but rather the new relationship that they have acquired with this ancient and everywhere reviled people of Israel. For the Christians in Macedonia and Achaia it must have been a very special privilege to collect money for people in the despised city of Jerusalem, which they themselves had held in contempt until very recently. In doing so, they learn that they are newcomers integrated into the old people of God. They now share in the promises to the Jewish patriarchs, and so they now also have to share their material blessings with their progeny.¹