Read the last two stanzas from "A Red, Red Rose" by Robert Burns.
'Till a’ the seas gang dry, my dear,
And the rocks melt wi’ the sun;
I will luve thee still, my dear,
While the sands o’ life shall run.

And fare thee weel, my only luve!
And fare thee weel a-while!
And I will come again, my luve,
Tho it were ten thousand mile.

Which poetic device does the poet use to separate the ideas in the first two stanzas of this poem from the last two stanzas?