LAYERS or LEVELS OF MEANING
When you read certain texts, it becomes clear that there are meanings there that seem to lie 'deeper' than 'on the surface'. These occur are when the writer has used language that develops imagery or connotations.
These 'layers of meaning' can be created in a text by the use of literary devices. A common literary device that creates layers of meaning is irony. When irony is being created, the writer says one thing, but you, the reader, are aware that something rather different is meant. Irony is like a subtle form of sarcasm.
There are several other ways to create layers of meaning in a text, for example, through the use of language that creates connotations, such as the literary devices of metaphor and symbol.
To appreciate a text's deeper levels of meaning it is necessary to reflect and interpret what you read and to notice when language creates emotion. A war poem, for example, might, on the surface, tell about life in the trenches, but at a deeper level might make a powerful case against war or against the propaganda being put out back home.
These deeper levels of meaning are used to help a writer develop the kind of emotion in the reader that helps create persuasive themes or messages.