Please mark and return wtih comments

[snow15145]

Jo snipped:

The Elder wand serves the author in two ways, firstly it allows 
Harry to reject absolute power as an option when he chooses HRX over 
Hallows, secondly it allows Voldy to be killed without Harry having 
to use an AK (explanation below).  
DD won the wand from Grindelwald, although we never learn how, and 
thereby gains its allegiance. Draco disarms DD at the top of 
Hogwart's tower but abandons the wand in his flight. However, the 
Elder wand has given its allegiance to Draco. How the wand 
recognises its true owner is never detailed and the only canon we 
have is that "the wand chooses the wizard".

Snow:

I agree with you Jo, that the wand chooses the wizard and recognizes 
who the true owner of the unbeatable elder wand is, whether or not he 
physically possesses the actual wand or not. 

As for the reasoning of how Harry was able to vanquish the bit of 
Voldemort in him without harm to himself, I envision that Harry did 
possess all three of the Hallows on or about the time that Voldemort 
attacked him the first time in the forest: 

Harry had the invisibility cloak but it was no longer on him at the 
time of the attack; Harry possessed the essence of the elder wand, 
who acknowledged Harry as the rightful owner, even though Harry did 
not brandish his wand at the time; And, Harry just recently accessed 
the stone's ability not even minutes before the AK was administered. 

Harry had had all three Hallows around him at the time of Voldemort's 
curse, which I feel may have gave him the invincible powers of the 
Hallow when he not only challenged death but willingly accepted it. 

The gravestone of the Potters had a quote:

"The last enemy that shall be destroyed is death" pg. 328 am. ed.

When Harry willingly accepted death he destroyed his enemy. Harry's 
enemy was the leach that became part of Harry's subconscious; the one 
that he remembered; the one he had access into emotions and powers; 
the enemy that was Voldemort's very soul. Harry willingly accepted 
death and was therefore protected from it. 

At Kings Cross, Harry could have decided not to go back to reality 
and Voldemort would still have been destroyed when Neville slain the 
remaining Horcrux, which was Nagini. 

Harry had a choice to return or not but when he did decide to come 
back, he already knew the battle would be won when the last Horcrux 
(Nagini) would be killed.

Harry actually won the battle in the forest!  When Voldemort issued 
the AK that destroyed the Horcrux portion in Harry, Harry won. 
Neville was directed to kill Nagini and Harry protected everyone else 
from the wrath of Voldemort by his selfless sacrifice. Voldemort was 
merely mortal again but with no power to lay even a finger on anyone 
who was protected by Harry's sacrifice. 

Snow