The meeting in Chapter 5 goes poorly; order seems to be slowly breaking down. Ralph is left uncertain about how to proceed, and begins to doubt his own judgments, as well as questioning if the Beast might actually be real. Jack's aggressiveness has made him a clear competitor for Ralph's authority, and as the group moves toward chaos, Jack's emotionally-charged reasoning makes him a more attractive figurehead for the uncivilized, moblike society that is emerging. Piggy knows that he will have no place in this society, and makes several pleas to Ralph, encouraging him to uphold his authority and the rule of law.
In regards to Jack's feelings, Piggy says that Jack respects Ralph, but mostly because Ralph can actually stand up to him and physically fight back. Jack also hates Ralph, and Ralph questions why.
“I dunno. You got him over the fire; an’ you’re chief an’ he isn’t.”
Piggy's reasoning is simple; first, Jack is jealous of Ralph's position, and second, Ralph had a valid and incontestable point when he criticized Jack and the hunters for their failure to keep the fire going. Jack has lost face and is in a vengeful mood.
Piggy's concerns also have an element of selfishness to them; he states that Jack, in wanting to hurt someone, will hurt Piggy if he can't hurt Ralph. Piggy knows that Ralph's authority is the only thing keeping Piggy safe, and so Piggy needs Ralph to continue in that role. Throughout the story, Piggy is used as a symbol of the more refined but physically weaker elements of "civilized" behavior, and his mistreatment is an analogy for the boy's descent into savagery.