They were pleased to do it, and indeed they owe it to them. For if the Gentiles have shared in the Jews’ spiritual blessings, they owe it to the Jews to share with them their material blessings. Romans 15:27
“The significance of the offering (the solidarity of God’s people in Jesus Christ) was primarily neither geographical (from Greece to Judea), nor social (from the rich to the poor), nor even ethnic (from Gentiles to Jews), but both religious (from liberated radicals to traditional conservatives, that is, from the strong to the weak), and especially theological (from beneficiaries to benefactors). In other words, the so-called ‘gift’ was in reality a ‘debt’…
The Gentiles must be careful not to be boastful or arrogant. They must rather remember that they have inherited from the Jews enormous blessings to which they have no title. In themselves they are nothing but a wild olive shoot. But having been grafted into God’s ancient olive tree, they ‘now share in the nourishing sap from the olive root’ (11:17). It is right therefore for the Gentiles to acknowledge what they owe to the Jews. When we Gentiles are thinking of the great blessings of salvation, we are hugely in debt to the Jews, and always will be. Paul sees the offering form the Gentile churches as a humble, material, symbolic demonstration of this indebtedness.”
John R. W. Stott in The Message of Romans: God’s Good News for the World (Bible Speaks Today; Downers Grove: IVP, 1994) 386-387.
What is the debt that all Gentiles pay? We are indebted to the Jews for the spiritual blessings we have received through Christ. This does not mean that we need to mail money our Jewish friends. It means we need to take a humble rather than an arrogant posture for the privilege of having been grafted into the family of God.
Even as we have been given a share in Christ, we must hold on loosely to all we have and take a sharing posture. This is the opposite of most Gentiles. Most hold for themselves. So really the debt that all Gentiles pay is one of gratitude and generosity for becoming partakers of the Spirit of God. Our only response is to be rich givers.