Just a friendly reminder to please post subject-specific threads in their respective subject forums.
Regarding the quote, it is the equivalent of the following in modern English:
"Then see the evidence of their evil with your own eyes".
The personification of the eyes in the original quote, which occurs by making them a witness, being a human characteristic/behaviour, enables the author to connect the reader with the object that is being personified (in this case, the eyes). This in turn enables the reader to understand/appreciate the existence of
"their evil".
I hope this helps!