Money, by its very definition, is never an end.
It is a way of exchanging, of acquiring things.
When it becomes an obsession, when it becomes an end in itself, that obsession is a slightly pathological situation.
This is true about anything.
Chewing is a way of eating.
When a person begins to chew before he eats, it is a sign of an illness.
Washing your hands is very important to cleanliness.
When you see a person washing his hands sixty times a day, it is a sign of compulsiveness.
Money is a way of transforming assets into other things, whatever they are.
If it becomes a purpose in itself, that is defined psychologically as a perversion.
This is exactly the definition of a perversion: in perversion, you have something that is auxiliary but that becomes a purpose in itself.
–Rabbi Adin Steinsaltz
From We Jews, p. 92, by Rabbi Adin Steinsaltz