People use one (or both) of two basic languages:
1. The vernacular or ordinary
2. Poetic language.
Our Blake spoke the poetic language from birth (as do most babies, but they unfortunately soon lose it). In many places ordinary language is understated: "I don't like him", may announce an intention of killing him.
In contrast poets are free to exaggerate. It may shock us into the truth they mean to convey. Blake was very, very good at that. Sometimes we just have to make allowances, but best of all is to be shocked into the truth.
Now which of these languages do we have here:
Good and Evil are deadly dreams that the Soul may fall into when it leaves Paradise following the Serpent.