חומש
There is a Mitzva learned in the Parsha, regarding the giving of Tzedaka. It is known that we have a kind of deal with Hashem.
If we give our מעשר כספים, ten percent of our earnings to charity, Hashem always finds a way to return this money to us. In a sense, we are allowed to even test G-d in this matter, and we will not be left empty handed.
However, when Yakov made his vow about giving מעשר to Hashem, he used the words, עשר אעשרנו לך, a double language of tithing. The Rabbis learn from this that Yakov was referring to double מעשר, or חומש. This חומש means a fifth or twenty percent of our earnings.
This so called deal does not apply when one gives more than חומש. Such a person is careless and wasteful, and is not leaving his family enough to live on.
The only exception to this rule applies to a very wealthy person. He is allowed to give even more than חומש, because of his great wealth.
All of this is learned from Yakov’s double language of עשר אעשרנו.