In the twenty-first letter of Igeret Hakodesh the Alter Rebbe highlights the importance of consistent and frequent giving of Tzedakah, rather than giving a lump sum once a year.
The Alter Rebbe explains that sustained habits of generosity transform the giver and bring the Shechina down into the world. The Alter Rebbe further illustrates how Tzedakah not only impacts the receiver but also elevates the soul of the giver, hastening the redemption.
-Igeret Hakodesh Epistle 21
-Class by Rabbi YY Jacobson