GRAND-DAD , they say you're old and frail,
Your stiffened legs begin to fail:
Your staff, no more my pony now,
Supports your body bending low,
While back to wall you lean so sad,
I'm vex'd to see you, Dad.
You used to smile and stroke my head,
And tell me how good children did;
But now, I wot not how it be,
The shorter last line with its refrain or  anaphora  ‘Dad’, gives emphasis to the important subject of the poem.
A Child To His Sick Grandfather