Byron uses the final couplet in each stanza to
a. create a punch line.
b. introduce the next stanza.
c. transition between characters.
d. state the theme.
b. introduce the next stanza.

Byron uses the final couplet in each stanza to 

a. create a punch line. 

Byron uses a specific poetic structure identified as Ottava Rima. It has a rhyme scheme of ABABABCC where each letter stands for the lines' end rhyme.  Its rhythmic pattern is in iambic pentameter. 

The couplet is represented by CC. These lines give a humorous conclusion to the six lines that come before it. In short, these lines are the punch lines.
 

1. lovingly and gently2.it shows that they feel warm feelings for them3.they provide background4.a strong executive is needed to lead the country