R'Ei ma'aser is riches

כב. עַשֵּׂר תְּעַשֵּׂר אֵת כָּל תְּבוּאַת זַרְעֶךָ הַיֹּצֵא הַשָּׂדֶה שָׁנָה שָׁנָה

 22. You shall surely tithe all the seed crop that the field gives forth, year by year.

The commentators take the command "Aser Ta'aser" (you must tithe) and teach a lesson on the results of following the Torah. "Aser BishvilShetis'asher " (Tithe so that you become rich).

Tractate Taanit 9a
Rabbi Yochonon met a young son of Reish Lokeish and said to him “Read to me your verse (that you are studying)”.
“Aser t’aser – Tithe, you shall tithe (Deutoronomy 14)”
“What is the meaning of (the double terminology, it is redundant)?”
“ (Read it as follows:) ‘Aser beshvil shetisasher’ - Tithe so that you will become (ashir) rich.”
“From where do you know this?!”
“Try it out yourself and see.”

 In actuality this connects with the statement of Pirkei Avos (Ethics of the Fathers) chapter 4 mishna 1:

 איזהו עשיר? השמח בחלקו. שנאמר (תהלים קכח), יגיע כפיך כי תאכל אשריך וטוב לך. אשריך, בעולם הזה. וטוב לך, לעולם הבא.

 Who is rich? One who is satisfied with his lot. As is stated (Psalms 128:2): "If you eat of toil of your hands, fortunate are you, and good is to you"; "fortunate are you" in this world, "and good is to you" in the World to Come.

  This means that it is not necessarily that when one gives his tenth to charity he will become wealthy (though that can happen), but that one who regularly gives tzedakah learns to consider that whatever he has is a gift from Hashem.  He learns to become "happy with his lot" and to live as if whatever he has is a gift and is not "coming to him". Thus, he learns the lesson and truly "becomes rich".

In truth, if someone puts aside his ma'aser (tenth) either into a separate account or even in a separate ledger and ensures that it is given to tzedakah (charity is not a good translation) he will find that
somehow he will actually be able to live on the remaining ninety per cent and that somehow there is enough money. I can testify to this because that is what happened to me.

The blessing is not that you suddenly get more money, but that whatever you have is enough for your needs.