The eye is the lamp of the body. So, if your eye is healthy your whole body will be full of light - Matthew 6:22
On the surface here, it appears that Jesus is telling us a psychological truth about perspective - that a positive attitude will make us more receptive to positivity in life. We will be more likely to see the glass half full rather than half empty.
While this interpretation is certainly true, it seems that there may be another meaning that is hidden from the surface. The word translated as ‘healthy’ in the original Greek is ἁπλοῦς. According to Theyer’s Greek Lexicon, this word means:
good fulfilling its office, sound
For this reason, many translations have interpreted this word ἁπλοῦς in a slightly different manner. The King James Version says:
“The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.”
This interpretation doesn’t change the meaning but rather gives us a better idea of what a ‘healthy eye’ actually looks like. Just two verses later Jesus tells us,
“No one can serve two masters, for either he will hate the one and love the other, or he will be devoted to the one and despise the other” - Matt. 6:24
Taking in the full context, it becomes clear that a ‘healthy eye’ is an eye that has its priorities straight. With two items in sight, it focuses on the more important one. If it is focused on both equally, then it is no longer healthy, for it is not giving proper attention to either one. Whatever we find ourselves focusing on most throughout the day is the God of our life.
Trust in the Lord with all your heart and lean not on your own understanding; in all your ways submit to him, and he will make your paths straight. — Proverbs 3:5-6