He that is rich need not live sparingly, and he that can live sparingly, need not be rich.
Franklin contrasts two ways of achieving financial ease. A wealthy person can afford to spend freely because substantial resources provide a cushion. Someone who is able to live sparingly, however, can achieve a different form of security by keeping expenses low. In that sense, reduced needs can lessen the amount of wealth required for a comfortable life.
The saying therefore treats wealth as partly relative to expenditure rather than simply to income or possessions. A person with modest resources may be financially secure if their needs remain limited, while greater wealth may be necessary to support a more expensive way of life. Franklin is not suggesting that poverty is harmless or that everyone can solve financial difficulty through thrift alone. His broader point is that controlling consumption can increase independence and reduce dependence on accumulating ever greater amounts of money.