Christie uses imagery to paint a picture of her characters..... she brings them to life with words.
Example of Imagery:
“Ackroyd has always interested me by being a man more impossibly like a country squire than any country squire could really be. He reminds one of the red-faced sportsmen who always appeared early in the first act of an old-fashioned comedy, the setting being the village green. They usually sang a song about going up to London.”
The Murder of Roger Ackroyd, pg. 7