Rosh Chodesh Av is the yahrzeit of Aharon the Priest. On a yahrzeit, "all the effort of man, for which his soul toiled during his lifetime... becomes revealed in a manifest way."
Aharon's service is associated with the Priestly Blessing which includes all possible blessings and possesses a unique dimension as clarified in Chassidic thought. That unique dimension becomes apparent through the comparison between prayer and blessing. Blessing has the advantage that it can bring about the manifestation of positive qualities, drawing them down into our lowly world. It, however, possesses a disadvantage in that it can only draw down influence that has already been generated; it cannot generate anything new.
In contrast, prayer has the potential to generate new influence. It, however, is limited in that the extent of its influence depends on the effort invested in prayer. The Priestly Blessing, however, combines both these qualities, generating new influence and hastening the manifestation of this influence in our material world. These qualities are more emphasized on Aharon's yahrzeit.
Aharon is associated with Moshe our teacher, "the first redeemer." Indeed, he served as Moshe's "mouth," i.e., he brought into revelation the qualities of Moshe who was "the first redeemer [of the Jews] and will be [their] final redeemer."
May this potential for redemption be revealed in our world, immediately, beginning with Aharon's yahrzeit. And this will be hastened by the distribution of money to tzedakah.