HBP theories...

[zgirnius]

No: HPFGUIDX 159879

> Eddie:

> I'm wondering why would Snape, upon seeing the battle, not join in? 
> Why would Snape even think that he should go up ONTO the top of the
> tower?  I may be wrong, but I don't recall any evidence that was
> available/visible to Snape to indicate that the top of the tower was
> important in any way.


zgirnius:
I gather that the Death Eaters were defending the foot of the tower 
stairs.. The Order members who describe the battle to Harry refer to 
Death Eaters going up and down those stairs, suggesting they control 
the access to the Tower. The voices Harry hears while onthe Tower, of 
Order members, sound like they are trying to get up the stairs. 
Another reason for Snape to suppose that something is happening up 
the stairs. This would make joining the battle a mistake. Unliek the 
others, he has a chance of getting up there without a fight, if he 
does not reveal his loyalties immediately by fighting one of the 
others. If he simply runs up the stairs, there is a good chance the 
other Death Eaters will accept that he is one of them and not stop 
him. (As in fact happened).