John Gill Commentary Proverbs 4:19

"The way of the wicked is as darkness: They know not at what they stumble." — Proverbs 4:19 (ASV)

The way of the wicked [is] as darkness They are in the darkness of sin, ignorance, error, and unbelief; their works are works of darkness; the way in which they are leads to eternal darkness, ruin, and misery, and so must be most uncomfortable and dangerous;

they know not at what they stumble ; they stumble at the word, which they are ignorant of, and at Christ, whom they have no knowledge of; and through the temptations of Satan and snares of the world, which they are not aware of, nor upon their guard against.