The reason for the rapture, is to resurrect
the just[ified] dead.

I Thessalonians 4:13-14
"But I would not have you to be ignorant,
brethren, concerning them which are
asleep, that ye sorrow not, even as others
which have no hope.
For if we believe that Jesus died and rose
again, even so them also which sleep in
Jesus will God bring with him."

In order for God to bring 'the dead in
Christ' with him, they have to be there
already, and they are by being resurrected
(raptured) previously.