Which sentence best explains Dante's intended use of symbolism in this passage?

Because their faces turned rount to their haunches

So that they were compelled to walk backwards

since they could not possibly see ahead

In Dante's passage, he's likely tries to explain that he is pertaining to compulsion of the sinners in their ways of looking backwards in a dark way in which they could see what they could do in the future in life. It is because the way how the passage is being said is that how the sinners way of life could bring them into a life that is full of darkness.