What is the importance of both etiquette and manner?

They say that etiquette and manners are the grease of society, they ensure that due to our relative population density, we do not irritate each other too much.

I think it stems from the "golden rule" Do unto others as thy would have done to thyself, this mixed in with traditional cultural behaviour leads to the formation of what is considered good etiquette and manners.

For example, burping in some societies is seen as rude, but others as a sign of appreciation for the food. You should follow the etiquette of the region as a testament to the golden rule, the reason it is there is down to cultural interpretation of that rule.

Its an interesting nuance of human interaction, and there is no real standard rule which is applied in all areas.