Wealth is not in an abundance of possessions; true wealth is the wealth of the heart.
ليس الغنى عن كثرة العرض ولكن الغنى غنى النفس
Laysa'l-ghinā ʿan kathrati'l-ʿaraḍ, wa lākinna'l-ghinā ghina'n-nafs.
Bukhari, Riqaq, no. 6446 (from Abu Hurayra).
The hadith sets wealth apart from things that can be counted.
It is not something one has seen, that a person is filled as possessions grow; more often the appetite grows along with them.
The wealth of the heart is being able to see what is in your hand as enough, and once it is gained, no scarcity can diminish it.
Seneca's definition of the poor man and this sentence come from two separate worlds and arrive at the same place.
The measure is not kept in a coffer; it is kept within a person.