We learn and refine the meanings of words throughout our lives. Children need to understand the sound structure of words and to know the meaning of many different words, as well as how to figure out word meaning from the context in which a word is used. Word skills are important as the foundation for learning to read.
Words have multiple meanings.
Take the word 'ear', for example. The most central meaning is the listening device on the side of your head. A less common meaning would be as in an 'ear of corn'. Figures of speech are important because they are very common in everyday speech and yet quite confusing to those who are trying to learn a language. Children need to develop some understanding of the sound system of words.