Q. If charity (tz’dakah) is a mitzvah, why don’t we say a b’rachah over it?
From the philosophical point of view, it all depends on what sort of mitzvah it is. If it is a mitzvah between man and man, it is assessed in relation to the other person. The nature of charity is such that if you had to wait to say a b’rachah, the recipient might collapse and die in the meantime. The mitzvah must be carried out at once.
What if it is a mitzvah between man and God? Can it be a mitzvah between man and God? Giving charity is because we have to love God, and loving His creatures is part of this love. Further, since He gives tz’dakah throughout the Bible, we humans, by means of our giving charity on earth, are walking in His paths.