The way of the wicked is as darkness: they know not at what they stumble.

Wesley's Notes

4:19 Darkness - Full of ignorance and error, of uncertainty and confusion, of danger and misery.

Matthew Henry's Concise Commentary

4:14-27 The way of evil men may seem pleasant, and the nearest way to compass some end; but it is an evil way, and will end ill; if thou love thy God and thy soul, avoid it. It is not said, Keep at a due distance, but at a great distance; never think you can get far enough from it. The way of the righteous is light; Christ is their Way, and he is the Light. The saints will not be perfect till they reach heaven, but there they shall shine as the sun in his strength. The way of sin is as darkness. The way of the wicked is dark, therefore dangerous; they fall into sin, but know not how to avoid it. They fall into trouble, but never seek to know wherefore God contends with them, nor what will be in the end of it. This is the way we are bid to shun. Attentive hearing the word of God, is a good sign of a work of grace begun in the heart, and a good means of carrying it on. There is in the word of God a proper remedy for all diseases of the soul. Keep thy heart with all diligence. We must set a strict guard upon our souls; keep our hearts from doing hurt, and getting hurt. A good reason is given; because out of it are the issues of life. Above all, we should seek from the Lord Jesus that living water, the sanctifying Spirit, issuing forth unto everlasting life. Thus we shall be enabled to put away a froward mouth and perverse lips; our eyes will be turned from beholding vanity, looking straight forward, and walking by the rule of God's word, treading in the steps of our Lord and Master. Lord, forgive the past, and enable us to follow thee more closely for the time to come.