If I earn $10 per month, have $20 in capital, and $15 in personal assets, how do you combine those numbers into a single number? What does that single number represent?
The number is called "net worth" and is slightly complicated if you're married or own a lot of illiquid assets. It also has debt and other liabilities subtracted so a house on mortgage or leased car, or company owned assets do not count, for example.
It does not count control of corporations and political power, which can be important as well. (But tend to go hand in hand to a degree.)
There's also gross worth which is a total lifetime worth. This would be high if you used for example expensive education. But then this one is much more nebulous.