User blog comment:FairyRaven/Why did the Celestial Spirits invite Lucy's group to the spirit world?/@comment-904888-20120724064034

Given that the entire party happened in a day in Celestial Spirit World, I doubt it was for the reasons you mentioned:

1. If they were trying to warn them about an impending danger, they did a really really bad job at it, since the spirits made absolutely no danger about it at all. 2. Jet and Droy not being present at the party could have just simply down to the fact that they were absent during the time frame which Virgo abducted them, rather than not joining them. Besides, it was supposed to be a party for those under Fairy Sphere's Stasis, which everyone at the beach, except Jet and Droy, was a part of. 3. Spirit King's remarks about the stars watching over you probably is a very simple good luck type farewell, something akin to 'God bless you', so I seriously doubt it would have any sort of double meaning. If anything, the King's line to Lucy is referring to the fact that she is the holder of their keys, hence why "We will always be with you", since it's almost literal for her case. 4. The spirits were probably so happy that Lucy is back that they either ignored the fact that they were training for GMG, or they simply overlooked that fact, hence why they still abducted them during their training.

With regards to 4, I have an alternate, but much more far fetched theory: They may, somehow, have contact with the members of Crime Sorciere, and know that they have the power to increase their powers for their GMG without having to commit the time for it, hence they were free to abduct them. This is supported by the fact that Ultear's pigeon landed on Erza (literally) very close to exact moment when they returned, and straight off, they offer them a way to increase their powers for GMG. If they didn't know that they were abducted by the King, they would have never been able to send the pigeons to them.