Why are symbols and motifs used in literature?

Symbols are what we use everyday even if we don't know it. You see symbols when you drive, when you're at school and even at home. Symbols make things easier to understand especially when you're reading a map. On a map there are lots of different symbols. For example, if there's a church, they don't write 'CHURCH', instead they put a cross to indicate there's a church. But sometimes it's hard to remember all of the symbols so sometimes they use colours. Areas with trees are coloured in green and lakes, rivers and oceans are coloured in blue.