“Who among you fears the LORD and obeys the voice of his servant? Let him who walks in darkness and has no light trust in the name of the LORD and rely on his God.” (Isaiah 50:10)
“Again Jesus spoke to them, saying, ‘I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.'” (John 8:12)
Jesus said, “I am the light of the world, Whoever follows me will not walk in darkness, but will have the light of life.” How is that consistent with Isaiah 50:10? The “darkness” in Isaiah 50:10 is not the same “darkness” in John 8:12. The darkness of Isaiah 50:10 is the courageous, hard path of obedience to the Lord, while the darkness of John 8:12 is abandonment by God, his face turned away, eternal death.
…setting Isaiah 50:10 and John 8:12 side by side is helpful. It suggests that walking through a dark season in this life, faithful to Christ, has more light to it than walking in the shining brilliance of our own brainstorms. It suggests that the darkness of obedience is better than the light of disobedience. God did not promise that we would never be confused and distraught; he did promise that he would never leave us or forsake us (Hebrews 13:5). Even when we can’t see him, he does surround us and guard us and lead us forward. We can expect moments in this pilgrimage when the only way into “the light of life” of John 8:12 is the “walking in darkness” of Isaiah 50:10. And which would we rather have — the “darkness” of faithful obedience leading to our vindication, or the “light” of self-will leading to endless miseries? That is the question of our existence.
-Ray Ortlund, Isaiah: God Saves Sinners, Preaching the Word, ed. R. Kent Hughes (Wheaton, Il: Crossway Books, 2005), 337-338.