The omniscient point of view is itself very important in helping to establish an air of normality in the story. As the story's told from the dispassionate standpoint of an all-seeing narrator not directly involved in the proceedings, we gain a sense that this annual ritual is perfectly normal for this small town at this time of the year.
In some respects, it's as if we're reading a work of anthropology in which a scientifically-detached observer is providing us with a privileged insight into the strange customs of a remote tribe. Only the members of the remote tribe in question happen to be the inhabitants of a small town in New England.
One could argue that the omniscient point of view makes the denouement when it comes all the more chilling. The lack of emotion provided by the narrator leaves a huge gap which is filled by our own shocked response to the disturbing revelation at the end.
Up until that point we'd been lulled into a false sense of security, led to believe that this was just one of those normal customs that take place in small towns across American every year. It's a beautiful summer's day. The sun is shining, the birds are singing, and everyone seems excited for the forthcoming lottery. What's more, the children are especially excited by the prospect of participating in this annual ritual. What could be more normal than that?