A thesis statement is one or several sentences that contain your essay's focus in a concise manner.

Example of a thesis statement:

By applying Bakhtin's ideas to literature, one can argue that T.S. Eliot's "The Burial of the Dead" (from "The Waste Land") has elements that align the work with both poetry and fiction; however, it still provides instances of intertextuality that one can find in all forms of literary writing. 

Example of a triplet:

If I were a dead leaf thou mightest bear;

If I were a swift cloud to fly with thee;

A wave to pant beneath thy power, and share (Percy Bysshe Shelley, Ode to the West Wind, verses 42-45)