Why some words in English are emphasized?

Why some words in English are emphasized?
= =\

Words are emphasized to draw attention to the meaning.This may be done through different punctuations on syllables,speed of talking,or different pitch between words.Emphasis can also be achieved through body language.Emphasis on words has several uses:
1.Draws attention,e.g.,You are GREAT.If you linger on the word GREAT,it draws attention to it.
2.Distracts other words,e.g.,You are GREAT that you hepled me.Lingering on the word GREAT lessens the amount of relative emphasis on the rest of the sentence,i.e.,that you helped me.
3.Imply contrast,e.g.,Albert,NOT BEN,is great.The phrase NOT BEN is emphasized to show contrast between the two people,emphasizing that Albert is great.
4.Convey emotions,different punctuations on words usually mean that the person is emotional,whether angry,sad,or excited.e.g.,I want to KILL you.