This Halacha is an excerpt from our Sefer
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Prior to all Holidays, a charity fund is to be established to provide those in need with the basic foods and delicacies needed for the Holiday. The necessity for such a fund applies especially prior to Shavuos. Each person is to contribute to the fund according to his ability.
 Hisvadyus 1988 Vol. 3 p. 390
 The reason: As everyone agrees on Shavuos one must be involved in eating a festive meal, and it does not suffice to sanctify the day just for G–d in doing spiritual matters and fasting.