22 The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. 23 But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness! (Matthew 6:22-23 KJV)
The eye is the light of the body
The preceding truths are illustrated by a fitting comparison. The actions of the whole body are guided by the light received through the eye. When the eye is clear and perceives objects as they truly are, the whole body is filled with light, and the person moves safely and properly. But if the eye is bad and sees things in a confused or distorted way, he stumbles in darkness, constantly at risk of losing his way or running into danger.
In the same way, an enlightened mind, recognizing things as they really are, allows a person to make sound judgments, wise choices, and conduct himself properly. But a darkened mind, which misjudges the true value of things, leads to mistaken choices. The more determinedly a deceived person follows his false understanding, the further he strays from the right path. If what someone considers his highest wisdom is actually foolishness—if his foundational belief is an error—then the light within him is really darkness. And how deep and destructive that darkness must be!
This directly applies to how people judge earthly and heavenly things. The worldly person starts with a wrong principle, so all his reasoning and calculations are flawed. The further he goes, the more dangerously lost he becomes. But this also applies to false religion. When what a person believes to be profound spiritual insight—whether from philosophy or misguided religious enthusiasm—is actually a deception, his so-called light is thick darkness from the depths of hell. Every conclusion he draws and every action he takes leads him further from God, truth, and holiness, sinking him deeper into error, prejudice, spiritual pride, and the trap of the prince of darkness.
As the eye represents our ability to judge, if our judgment is sound, our actions will be guided by wisdom. But if our judgment is clouded by error, our whole life will be affected negatively. Misguided understanding leads to calling evil good and good evil, which is disastrous for the soul. This is a serious and common danger. How carefully, then, should we examine our guiding beliefs against the word of God, praying earnestly for the teaching of His Holy Spirit!
The eye being single can also refer to our focus and ultimate purpose as Christians. If we aim only at pleasing God and living a life that brings him glory, our path will be bright and sure. But if we try to serve God while seeking our own selfish interests, our lives will be unstable. The hypocrite, like a rower who looks one way while rowing another, appears to serve God but is preoccupied with material things and earthly gain.