The surprise of Isaiah 50:10 is that the kind of person in view is further described as the one who walks in darkness and has no light. Fearing the Lord and obeying the servant would seem naturally to imply walking in light. What the Lord means, however, is not the ignorance or blindness of the human understanding, but the afflictions by which the children of God are almost always overwhelmed.
1 Servant-followers will share in the experiences of the Servant, walking with him into the darkness of frustration, injustice, humiliation, and abuse.
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10 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.