Many thanks to everyone who's written back to me after my request for
whatever facts were *known* about the Human Instrumentality
(Complementation/Completion) Project from the Evangelion anime ...

Here's my version. Fasten your seat belts, this could get bumpy.

(WARNING!! Massive spoilers ahead! Stop reading now if you haven't seen
all of Neon Genesis Evangelion yet and want to figure all of this out for
yourself! This is your final warning; the following information may or may
not actually be true but it gives away a *lot* about what I think is going
on in the final story arcs of the Evangelion anime. If that doesn't
dissuade you - or you've already seen all of Evangelion and want to see my
reasoning - then by all means read on.)

<{([ start ])}>

	Put simply, the Human Instrumentality Project was a process by
which the minds and spirits of all human beings were linked together into
a single immense transphysical being, so that the whole of Humanity could
finally enter Heaven. This is what SEELE and Lorenz Kiehl have apparently
had in mind from the beginning; it's just the 'how' that's been confusing
everyone. 
	First off, even when the HIP was implemented, people retained
their individuality even though their minds and souls were being linked
together. I suspect that the images from episodes 25 and 26 (which I
haven't *seen* yet, just read about) are yet another look inside Shinji's
mind while the Project is being put into effect.
	The other question is, why bother with something like this? If
people retain their individuality, why even try to join their hearts and
minds? Two reasons: first, the strengths of the whole can serve to
reinforce and balance the weaknesses of the individual. I suspect that the
later Angels were working towards this goal themselves, which would
explain the mental-contact aspects of Reliel, Arael, and Armisael (the
12th, 15th, and 16th Angels): they were indeed testing the human psyche,
with the three Eva pilots as examples. Bardiel (the 13th Angel) may have
been attempting this as well, although I can think of another possible
reason for infecting Eva-03.
	The second reason is demonstrated by the Third Impact, in End of
Evangelion. There are apparently two keys to the start of the
"constructive" Third Impact: Rei's merging with Lilith, and the
transformation of Eva-01 and SEELE's mass-production Evangelions. As far
as I can tell, Rei's merging with Lilith was just the trigger for the
second phase of the Human Instrumentality Project, the gathering of all
human souls into a single entity - but the Third Impact itself, which
*released* those souls, couldn't have happened without the Evangelions on
the surface. (Unless of course a freed Lilith was able to find Adam and
release him ... which in all likelihood would have set off the Third
Impact either way.)

Feel free to poke holes in my reasoning, but this is the best explanation
I can think of ... (and I haven't *seen* episodes 25 or 26, or the End of
Evangelion movie, yet.)