If your eye is pure, there will be sunshine in your soul. But if your eye is clouded with evil thoughts and desires, you are in deep spiritual darkness. And oh, how deep that darkness can be!
EXPLANATION: Spiritual vision is our capacity to see clearly what God wants us to do and to see the world from His point of view. But this spiritual insight can be easily clouded. Self-serving desires, interests, and goals block that vision. Serving God is the best way to restore it. A “pure” eye is one that is fixed on God.
Also On Spirit 1340: