The holiday of Shavuot is one of the best times for giving charity on behalf of departed loved ones and is part of the holiday Yizkor prayers. Yizkor is the Jewish memorial service recited four times a year in synagogue. It’s a time to reflect on the divine, eternal nature of souls, pray for them and pledge to give charity on their behalf.
As a side note, the Book of Ruth is also read in synagogue on Shavuot along with other Torah readings. The question is, what is the connection between the story of Ruth and Shavuot which is a celebration for receiving the Torah on Mount Sinai?
Rabbi Ze’ira asks why the Book of Ruth was written altogether. He explains that although there are no Jewish laws taught in the Book of Ruth, the Torah included it in the scriptures just to underscore the acts of charity and loving kindness conveyed throughout the story of Ruth. On Shavuot we read about how Ruth espoused and personified Torah values for Torah is all about loving-kindness, as the verse states (Proverbs 31/26), “and instruction of kindness is on her tongue.”
Jewish sources teach that it’s a big mitzva to give tzedaka on behalf of a departed loved one. The soul living in the afterlife derives much benefit and elevation while the one who gives yizkor charity on its behalf receives much blessing and prosperity.
The best time to give the yizkor tzedaka is before the holiday. This way you can be sure you don’t forget to give your pledge. Not giving pledged tzedaka has negative ramifications and is treated stringently in Jewish law.
There’s also a segula to being proactive when it comes to doing mitzvot. In the book of Iyov (42/3) it says, “Who came ahead of Me, I will pay his reward.” Rabbi Tanchum bar Abba teaches that when a person who currently doesn’t have much money gives charity, or a person who doesn’t own a home yet buys mezuzot in advance, Hashem pays them for it! So giving charity whether for Yizkor or not is the best win-win and segula for having lots more to give.