thick darkness: dark heavy enough that a person cannot see the way, and the disaster that such dark stands for
Hebrew has a whole family of words for the dark, and this is one of the heavy ones. The everyday word for darkness (חֹשֶׁךְ) simply names the absence of light. This word names dark with weight in it, dark that presses on a person. Exodus can even lay the two words together and call the ninth plague on Egypt a darkness of thick dark, three days of blackness in which no one in Egypt could see anyone else.
Almost everywhere it appears, someone has lost the ability to find the way:
- a whole nation groping at noon the way a blind man gropes
- the wicked stumbling over what they never saw coming
- lying prophets sliding on a slippery path they cannot see
The dark here is never scenery. It is the reason a person does not arrive.
That is also why the prophets reached for it to announce the day God settles accounts. Joel and Zephaniah describe that day in the same four words: a day of darkness and thick dark, a day of cloud and heavy cloud (עֲרָפֶל). The dark of judgment is the same dark as the plague and the same dark as the ruined path, now spreading over a whole world.
Isaiah takes the word the other direction. To people who say they hoped for light and got dark, and who walk in deep gloom in broad daylight, he promises that their thick dark will shine like noon. The word itself does not soften. It is simply reversed.