John Piper wrote an excellent article on his website, Desiring God, answering this question.
What does the bad eye refer to in Matthew 20:15? It refers to an eye that cannot see the beauty of grace. It cannot see the brightness of generosity. It cannot see unexpected blessing to others as a precious treasure. It is an eye that is blind to what is truly beautiful and bright and precious and God-like. It is a worldly eye. It sees money and material reward as more to be desired than a beautiful display of free, gracious, God-like generosity.It's all about perspective.
My contact lenses were so dirty yesterday that I thought every room in the house was smoky. We often have hazy, smoke-filled days in summer due to forest fires. But, when I asked the kids if it was smoky, they said, "No." So, I took my contacts out and put them in a cleaning solution overnight. No more foggy, blurry vision! Amazing how in my perspective I assumed that the whole house was in a haze, when it was really just my eyes.
I know my eyes are bad, physically, due to genetics. If I don't wear corrective lenses, I am legally blind. It's not a good thing when the corrective lenses are "bad" or dirty.
How much worse is it when my spiritual eyes are bad, due to sinful nature? Then my perspective is filled with sinful thoughts, causing me to perceive and react in wrong ways. I need the cleansing, restoring work of the Holy Spirit to bring light to my mind, body, and soul.
