St. Paul organized a collection among the churches of Asia Minor for the starving Christians of Jerusalem. When visiting these churches, Paul publicized the generosity of the poor Macedonian church to spur his hearers to also give generously (see 2 Cor 8:1-4, 8, 24; 9:2-5; 11:9). Paul knew that generous giving reflects the inner trust a person has in God and shows to others "the proof of [their] love" (2 Cor 8:24; Phil 4:15-17).
Though Jesus tells us to keep our deeds of mercy secret (Mt 6:2-4), Paul challenged churches to grow in generosity. Paul wanted his flock to give openly, "for all the churches to see" (2 Cor 8:24). He was "concerned not only for God's approval but also for the good esteem of men" (2 Cor 8:21). Paul was not trying to encourage competition, but rather fraternal generosity.
Paul's public disclosures about the generous giving of other churches resulted in an increase of zeal among Paul's hearers to give generously (see 2 Cor 9:2). He also warned the Corinthian church that he might send along some members of the Macedonian church to observe their collection (2 Cor 9:4). This would give tangible evidence to the Macedonians whether or not the Corinthians had any "trust" in God (2 Cor 9:4).
We might cringe at Paul's appeals. But he would cringe even more at our modern fund-raising methods. The Church in America often raises money with appeals to gambling, games of chance, and sales of alcohol. Paul used preaching, teaching, and an appeal to personal and communal accountability. Guess whose methods resulted in an increase of both generosity and faith?