From Ohr Avigdor Shaar Bitachon by Rabbi Avigdor Miller
If you trust in Hashem, you know that the money you earn is not really yours and therefore you should manage it wisely as an agent for Hashem.
The money you earn is not really yours
What does that mean in practice? If you make a thousand dollars a week and you need only eight hundred dollars to live on, you don’t automatically give away two hundred dollars, but you manage it in a responsible way. Give the appropriate maaser (tithe) to charitable causes and put away what you will need to cover anticipated future expenses. That which you save should be prudently invested, for you are acting as Hashem’s treasurer.
We find that pious people are very careful about their property, and seek to increase their assets in a prudent fashion. Remember that you are holding the money for Hashem, so you may not waste it or give it all away.