Ralph's speech tells us that he's devoted to the establishment of a rules-based order of civilization on the island. He knows that if the boys are not just to survive but thrive on the island, they're going to have to create a system of rules and abide by them. As the boys are far away from civilization, it would be all too easy for them to degenerate into outright savagery. Ralph's all too aware of the dangers of this, which is why, in his speech, he tries his level best to impress upon the other boys just how important it is that they adhere to the values that their privileged upbringing has instilled in them. Although Ralph's still only a boy, and like all the other boys on the island initially experienced a great thrill of being free from adult supervision, he still has the maturity to realize that being stranded on the island isn't a game or a big adventure.
Ralph's speech in chapter five is his assertion of his leadership and role of chief; he feels his responsibility as leader keenly. Moreover, Ralph sees it as his duty to the other boys to facilitate their rescue and general well-being in any way possible. This moment comes shortly after Jack has led the other boys away from their post at keeping the fire lit and a potential rescue ship passed by the island.
Ralph reminds himself that this meeting must be all about business-- he reinforces the rules and does his best to remind the other boys that rescue must be their primary objective. Golding uses this scene in the novel to reveal Ralph's ties to civilization and his earnest belief in rescue, but also to affirm the morality of Ralph's character. Above all, he is a boy who wants to do the right thing and innocently expects the other children to share in his values.