Against Eternal Darkness

The Collector pondered exactly how to state what the purpose of these goblin specimen were. They desired one, and the Collector was in a position of authority to grant them one.

Or, rather, it was more accurate to state that the Collector could suggest them a purpose, and though they would undertake it due to the Collector's perceived authority, it was up to them whether they would truly believe the purpose suited for them. 

To that end, the Collector was incentivized to create a purpose for them that would grant them sufficient satisfaction.

Perhaps, as the elder had stated, a promise to an "Old Age" which the Collector deduced based off conversational hints and terminology that it was an era within which the goblin species was both more numerous and influential.