How does Graham Greene use imagery in The Power and the Glory?

Imagery:

"Mr. Trench went out to look for his either cylinder, into the blazing Mexican sun and the bleaching dust. A few vultures looked down from the roof with shabby indifference: he wasn't carrion yet. A faint feeling of rebellion stirred in Mr. Trench's heart, and he wrenched up a piece of the road with splintering finger-nails and tossed it feebly towards them. One rose and flapped across the town: over the tiny plaza, over the bust of an ex-president, ex-general, ex-human being, over the two stalls which sold mineral water, towards the river and the sea."

"Something you could almost have called horror moved him when he looked at the white muslin dresses - he remembered the smell of incense in the churches of his boyhood, the candles and the laciness and the self-esteem, the immense demands made from the altar steps by men who didn't know the meaning of sacrifice. The old peasants knelt there before the holy images with their arms held out in the attitude of the cross: tired by the long days labor in the plantations they squeezed out a further mortification. And the priest came round with the collecting bag taking their centavos, abusing them for their small comforting sins, and sacrificing nothing at all in return - except a little sexual indulgence."