How did Willie managed to learn all of the lines of the play in Chapter 13?

Willie repeated the lines over and over in order to learn them.

"Bah! 'Umbug!" he cried as he paced the floor. It was at least the fiftieth time in the past hour that Willie had uttered the words. He paused and read the nephew's lines, put down the script and began pacing the floor again. "If I could work me will, every idiot who goes abaht wiv Merry Christmuss on 'is lips should be boiled wiv his own puddin', and buried wiv a stake of holly through his heart. He should!"
Willie sat down on the end of his bed and gave a sigh. "I nearly got it," he muttered to himself. "I got to be a bit more grumpy." He rose.
"Nephew!" he said brusquely. "You keep Christmuss in yer own way and let me keep it in mine."

He stopped and hit the open palm of his hand with his fist. "No! It don't feel right. I'm a bad-tempered man and I don't like bein' interrupted, like." He began again. "Nephew, you keep Christmuss in yer own way and let me keep it in mine."
A loud knocking at the front door made him jump. "Blow it!" he grumbled. "Jes' when I wuz
gettin' it." He frowned and walked towards the trapdoor. Immediately he realized how
Scrooge must have felt when he was interrupted.