system
Given the following post, respond as if you're commenting on Reddit:
human
[XCOM] What did the aliens want with the humans?

spoilers: its revealed at the end that the Ethereals wanted human psychic ability, and had been modifying various other species for that purpose. But why? What were they going to do wth the humans once they had them available?
gpt
*Massive Spoilers.*

Short Version:  It was the biggest and most extreme tough-love project in the Galaxy. 

Longer Version:  The Ethereals identified shortcomings in their makeup.  They attempted to transcend mortality, but somehow failed.  Psychically strong but physically frail, they self-diagnosed as imperfect and flawed beings.  So they went around to try and create the perfect being.  Most of the beings fought by the XCOM teams were failed experiments at creating a perfect being that could achieve what they could not - ascension.

The Sectoids were too frail and too cruel, the Mutons too dumb, the Floaters too machinelike, the Thin Men unable to use psionics.  All imperfect in some way.

And then came their invasion of Earth.  The XCOM project succeeded where the Ethereals had failed, creating a soldier who was equally physically and psychically gifted.

Of course, the Ethereals had then hoped to guide the fledgeling next evolution of humanity, taking the perfect being forged in the fires of invasion and preparing them for "what lies ahead".  
Unfortunately, the Commander of the XCOM Project had other ideas...