Why will Asamecha (your storehouses) be full?
R. Yonah: This is like it says "uv'Chanuni Na b'Zos" (Mal'achi 3:10. Hashem promises to reward one who gives Ma'aser.) This is the reward for "Kabed Es Hashem me'Honecha."
Malbim: If you believe that the beginning of all things are from Hashem, then He sends Brachah on all your deeds. If you are "Yere Es Hashem v'Sur me'Ra" (7), to do according to His commands, all your conducts will be blessed.
Why will your winepresses overflow?
R. Yonah: This corresponds to "me'Reishis Kol Tevu'asecha." Tevu'ah can apply to wine - "u'Sevu'as ha'Karem" (Devarim 22:9). It mentions increase regarding the winepress, for Brachah is found in something not measured (only in what is Samuy (hidden) from the eye - Ta'anis 8b). A part of Bitachon is confidence that when he detracts from his money for a Mitzvah, it will increase. Chazal said, salt (the preservative) for money is to detract (give to Tzedakah); keeping money to preserve it for himself causes loss (Kesuvos 66b). 1
The Gemara learned from "ha'Brachah ba'Asamecha" (Devarim 28:8).
