Question about Barty Jr.!Moody teaching Harry

[Diana <dianasdolls@yahoo.com>]

No: HPFGUIDX 48650

I've done some preliminary looking, but haven't found a post that 
addresses this question.  I'm sorry if it's been discussed to death 
already...this only my second post to the group.

When Barty Crouch, Jr. was disguised as Mad-Eye Moody and teaching 
Defense Against the Dark Arts to all the Gryffindors, including 
Harry, why did Barty Jr. "teach" Harry to throw off the Imperius 
Curse?  

I realize that Harry has a natural talent for resisting the Imperius 
Curse in the first place, but why would Barty Jr. put Harry through 
his paces "four times" until Harry could throw it off entirely?   
This lesson left Harry completely prepared to throw off Voldemort's 
attempted Imperius Curse at the end of GoF.

Taking into account that Barty Jr. needed to deliver Harry alive to 
Voldemort for his spell-to-get-his-body-back to work, Barty Jr. 
still seemed to teach Harry and his classmates quite a few things 
that ended up helping Harry when he was facing Voldemort at the 
end.  I know that Barty!Moody had to appear and act like the real 
Moody, but he was working for Voldemort the whole time and wouldn't 
seem to want to teach Harry useful things that could help Harry 
*fight back* against Voldemort.  

I've just reread GoF and Barty!Moody's practical (and quite useful) 
lessons still puzzle me.   The only explanation I can come up with 
is that Barty!Moody thought Voldemort might have preferred a longer 
and therefore more *entertaining* duel with Harry?  Or maybe Barty!
Moody thought someone else [not Voldemort] might have used the 
Imperius Curse on Harry that would have ruined Voldemort's plans?   
Or, my current front-running theory, is that Barty!Moody thought 
showing the Three Unforgivable Curses to Harry would frighten him 
more, thus leading to more pleasure for Voldemort and pain for 
Harry?  After all, knowing what horrible thing is coming is much 
worse than not knowing to be afraid at all.  This last theory makes 
Barty!Moody a very unpleasant and nasty character, even more than 
before.  

Anyone care to share their theories? :)

Diana