1. What in the chapter “The Shell and The Glasses” is the human meaning of Jack’s raid?

Jack and his group do not take the conch from Piggy.  In
fact, Piggy is holding the conch when he dies:  "The rock struck Piggy a glancing blow
from chin to knee; the conch exploded into a thousand white fragments and ceased to
exist."  

When Jack and his group first raid Ralph's camp
earlier in Chapter 9, they take fire.  In the subsequent chapter (The Shell and the
Glasses), they take Piggy's glasses.  It's important to note that Jack does not want or
need Piggy's conch.  The conch represents a democratic order, a type of organization in
which anyone can have a say, a voice.  Jack rules his tribe as a dictator.  He makes all
the rules.  Unlike Ralph, he does not seek input from the group when decisions are
made.  During this raid, Piggy mistakenly believes that Jack wants the conch.  However, 
Jack really wants Piggy's glasses.  When he has these in his possession, "he was the
chief now in truth."  His group is completely independent of Ralph's because now he can
make fire on his own. 

Piggy's glasses do to some extent
symbolize intelligence and rational thinking.  But when Jack has them, they represent a
means to create fire for cooking, and later in Chapter 12 fire becomes a weapon.  Jack
rules by whim, not rationality, so when Jack holds the glasses, their previous
association with intelligence is lost. Now they represent a means to satisfy more primal
instincts.  This raid is particularly important in that Jack  assumes complete dominance
on the island.  With glasses in hand, he does not need Ralph or Piggy.  He has the
island under his control.  He can  have Winfred tortured at will; he can hunt as he
pleases; he can have feasts; he can kill whomever he deems his
enemy.