From the moment Jack Merridew appears on the stage with an air of "superiority and off-hand authority" with his chorus boys, even as Ralph is already presiding over a meeting of a group of others rescued on the island, it is obvious that power is going to be a major issue in the novel.
Power is sweet and Jack and Ralph love it. Like all those who love it, they both equally lay claim to it but by different means and for different reasons. While Ralph relies on the privilege of holding the conch, Jack in turn exploits self-assertion as he says with brazen arrogance: "I ought to be chief... because I'm chapter chorister and head boy".
Through a popular vote the other boys elect Ralph their leader simply because of his size, his attractive appearance and, most importantly, because he has the conch although Jack seems to be the most obvious leader. This democratic process shows that power belongs to the people who take it away from or choose to give it to whoever they want. This is also demonstrated when Ralph again overwhelmingly defeats Jack in the second leadership contest unnecessarily forced on the boys by the rebellious Jack.
Power in the novel manifests itself in two distinct forms - inclusive and integrative. The inclusive form allows for power sharing arrangement. This is why Ralph insists on the use of meetings and dialogues to get issues resolved. It also explains why he wants to bring Jack on board by conceding to him the leadership of the choir boys after defending him in the struggle for power but power is also used to foster social cohesion and advance the cause of the people. For this reason, Ralph is earnestly concerned with the welfare of the boys and their immediate rescue.
On the other hand, power can be used autocratically as an end in itself. In this case, it is primarily wielded to advance the myopic interest of the ruler. Jack after seizing power builds a cult of personality around himself and unleashes a reign of terror on the island. The development is regretted and bemoaned even by Roger, his second-in-command. In the process, Jack leads his hunter boys from Rock Castle to the Beach Platform to destroy the shelter under construction, molest Piggy the voice of reason, and steal his glasses. It is also the same reign of terror that prematurely terminates Piggy's life in their wild and. maddening chase to kill Ralph.
Power corrupts as shown by Jack but when it is seen as an effective means to a useful end as demonstrated by Ralph, it is desirable.