But we don't want you to be ignorant, brothers, concerning those who have fallen asleep, so that you don't grieve like the rest, who have no hope.
Concerning them that fall asleep ...  This should not be understood in the limited sense of "have fallen asleep" (KJV), because it purposely included those already dead and others yet to die before the coming of Christ.  Paul had not departed from Thessalonica a very long time before these lines were written, but already the death angel had descended upon the homes of some of the Thessalonians, accompanied by the inevitable grief precipitated by such an event.