Many years ago I read this book titled "We Shall Judge Angels"
by Harold Chadwick which I found to be rather enlightening, though
I would disagree with him on some finer details. But I think the
overall premise is right on the money! Let me explain briefly.
God knows all things from the beginning to the end. So why still
go on with the whole thing? We have the created order, the
spiritual powers and authorities (angels, and those that later
rebelled) and the earthly creations (man and animals etc). All
were perfect and without sin after God has created them and called
it very good. Yet between then and Adam's fall there was the fall
of Satan and the angels that rebelled. Here you have a class of
free-willed spirit beings higher than man, who rebelled against
God. These were cast out of heaven, some bound in chains (tartarus)
while others were allowed to roam the earth (the evil
spirits/demons), and of course the devil himself. And there were
those angels who did not rebel against God.
Through humans, who did not possess any powers like the angels,
God worked through their eventual rebellion and sin to redeem for
Himself a people (the Bride) for Christ. And through this imperfect
people (the Church) who were created "lower than the angels" God
will show all the angels (fallen or not) the riches of His glory
and manifold wisdom and the depth of His love through
Christ Jesus. At the end when the curtains of history are drawn,
all creation will finally see the big picture (the eternal purpose
of God) and give praise to God for all that He has done, and
understand and appreciate the wisdom of God through all the ages.
Nothing was done in vain. It was to be like a "show" to the angels,
the created spirit beings (esp the fallen angels) how foolish they
were to rebel against God.
This in a nutshell sums up what I believe to be the "why" to
your question. There's more to be said but for that you would have
to read the book!
Hmmm....nice point of view....Thanks for explaining...