How does John Bunyan use imagery in The Pilgrim's Progress?

Imagery:

So he commanded his man to light the candle, and bid Christian follow him: so he had him into a private room, and bid his man open a door; the which when he had done, Christian saw the picture of a very grave person hang up against the wall; and this was the fashion of it. It had eyes lifted up to heaven, the best of books in his hand, the law of truth was written upon his lips, the world was behind his back. It stood as if it pleaded with men, and a crown of gold did hang over his head."

"By the going up of the fire we are taught to ascend to heaven by fervent and hot desires. And by the sun, his sending his heat, beams, and sweet influences downwards, we are taught that the Saviour of the world, though high, reaches down with his grace and love to us below."