They were setting up the corruption of Sinestro.
I mostly enjoyed the movie with several exceptions.
Parallax, the evil cloud; was a poor villain for an action flick. I also thought that OA, the home of the Guardians and the center of the universe was poorly portrayed as a barren rock.
Parallax was too soon. He should not have been the first villain. He would have been a much better third movie villain or possibly a side story to the Darkseid encounter for Justice League.
They way I think they could have done it was have the first movie teach Hal Jordan how powerful the ring was and show terrible results that can happen if the ring is misused. Maybe have Hal Jordan accidentally set off a natural disaster that threatens a town or a city and he fights to make it right. The second movie, shows him growing as a Lantern and something happens in the second movie that causes Sinestro to lose confidence in the green ring, causing him to steal the yellow ring. In the third movie, they have their showdown.