What this 'earn' mean?

Question

Enter, stranger, but take heed
Of what awaits the sin of greed,
For those who take, but do not earn,
Must pay most dearly in their turn.
So if you seek beneath our floors
A treasure that was never yours,
Thief, you have been warned, beware
Of finding more than treasure there.

(from Harry Potter and the Sorcerer's Stone)

I guess ‘take’ and ‘earn’ both take implicit common object (a treasure or something). And ‘earn’ means ‘to deserve or get (something)’–– If there were intransitive examples in dictionaries for ‘take’, I might have thought ‘earn’ is ‘to get money for work that you do’. Are my guesses all right?

Answer 1

Your surmise is correct. The verse is speaking not of those who take or earn something in particular, but of taking-without-earning divorced from particular objects.

This sort of omission is very common in gnomic or proverbial speech:

Buy ∅_OBJ low, ∅_CONJ sell ∅_OBJ high.

To err is human, ∅_CONJ to forgive ∅_OBJ ∅_VERB divine.

Garbage in ∅_P-OBJ ∅_VERB, garbage out ∅_P-OBJ

Answer 2

You are correct, the poem is addressing those who take a thing that they did not earn; that is, they take something that does not belong to them, something they should not have: in brief, a thief (as spelled out farther along in the verse).

As I recall, this is at the entrance to Gringott's Wizarding Bank, and it is letting would-be robbers know that there are strong security measures in place, so they will be caught (or possibly injured or killed) in the course of their attempt to steal.

Answer 3

For those who take, but do not earn,

This phrase describes those who consume but do not produce anything that others want. They are, in the venacular, leeches, mooching off of those who do actually create and work. The poem goes on to say that these lazy good-for-nothing takers-but-not-makers will eventually have to pay.