Chazal (Bava Basra 9) teach us, יותר המעשה גדול העושה מן, "Causing others to give tzedakah is a greater mitzvah than giving tzedakah yourself." This means, in addition to giving tzedakah, there is a particular benefit in going around and asking people to give tzedakah to those in need.
There is a halachah that one must stand up for someone performing a mitzvah. Therefore, the Pischei Teshuvah (Yorah Dei’ah 256:1) writes, "One must stand up for the gabai tzedakah while he collects money for the needy."
Perhaps this is one of the reasons people stand during דוד ויברך. During this part of the tefillah, the gabai often goes around the beis medresh collecting money. Therefore we should stand for him as he is performing a mitzvah.
Rebbe Elimelech of Lizhensk zy'a says, "Going around the four corners of the city to collect money for the poor atones for severe sins that deserve the four deaths issued by beis din."
Reb Aharon of Belz zy'a said, "Going from door to door collecting money for the poor frees a person from kares." The shame one endures by performing this mitzvah atones and purifies.
The Aruch HaShulchan (247:5) writes, "I received a kabalah that when one collects money for others, this protects his future generations that they will never need to collect money for themselves."
Reb Getzel Berger z'l from London (niftar 1977/ח"תשל) was a wealthy Satmar chasid who gave large sums of money to tzedakah. The Satmar Rebbe zy'a once asked him that he should encourage other rich people to donate to tzedakah in addition to giving tzedakah. Reb Getzel replied that he preferred to give more money for tzedakah than to solicit others, but the Rebbe insisted that he also ask other wealthy people for donations.
