Paul receives a donation from the Philippians, and he gives thanks for their remembrance of him (Philippians 1:3). But the thanks is not offered to the Philippians; it is offered to God. He considers no man his benefactor; he has no debt to anyone but to love.
This is new, according to Peterman ( Paul’s Gift from Philippi: Conventions of Gift Exchange and Christian Giving (Society for New Testament Studies Monograph Series) ): “Divine reward does not enter into Greco-Roman social reciprocity” (89).
The change is epochal. Greeks and Romans believed they were in reciprocal relations with the gods: do ut des was a principle of religion not just social life. But for Greeks and Romans religious and social reciprocity were kept separate. Benefits and services between men were “secular.”
In the new economy of the gift, with the Christian gift and Christian gratitude, there is no secular gift. Gifts create partnership in the gospel and thanks is owed to the God of the gospel.