What does 'in their turn' mean in this context?

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)

What does ‘in their turn’ mean?
(It seems like ‘when their turn comes’. But there are dragons and traps beneath the bank’s floors, so as soon as they try and rob something they would be snapped away or trapped. That is, there would be no time lagging. So I suspect there might be some other meaning for ‘in their turn’.)

Answer 1

A bit of "poetic license" is often necessary in order to make a poem have correct rhyme and meter. In this case, "in their turn" is simply a way of saying "when the right time comes"; as you say, that time may be immediate.

But there may also be delays; if you manage to avoid getting zapped by the vault door, you can take as long a break as you want while packing up the gold before you have to confront the dragons at the next security checkpoint. And if by some miracle you do escape from the vaults entirely, there's still likely to be a team of bank enforcers hunting you down eventually, so "your turn" (to be punished) will still come, and then you will "pay most dearly."

Answer 2

In their turn

In this instance, those who are lazy will, eventually be made to pay. "In their turn" is equivalent to "in due time" or "eventually" or "at some point in the future."

Answer 3

"in their turn" is mostly shortened to "in turn". The Free Dictionary gives a good overview of the use of this expression.

http://idioms.thefreedictionary.com/in+turn

I would say "in their turn" has the sense of "for their part".