For the morning is to them even as the shadow of death: if one know them, they are in the terrors of the shadow of death.
They shrink from the "morning" light, as much as other men do from the blackest darkness ("the shadow of death").
If one know - i:e., recognize them. Rather, 'they know well (are familiar with) the terrors of,' etc. (Umbreit.) Or, as Maurer. 'They know the terrors of (this) darkness'-namely, of morning light, that it is as terrible to them as darkness ("the shadow of death") is to other men.