Haughty eyes and a proud heart,
the lamp of the wicked, are sin.
Scripture makes clear God's displeasure of pride which is the root sin of the wicked. They will not humble themselves before God. This is played out in various ways, most notably through the violence committed against others.
The proverb reveals how pride mars their perspective on reality. Pride is the lamp by which the wicked see what is outside themselves. What do they see? They see people to despise who don't measure up to their distorted standards. Conversely, they see others to admire who in reality model arrogance and wickedness. A notable author whose works are rife with licentious sex visited a city noted for its licentiousness. Whereas most people would see the obvious vulgarity, broken lives, and despicable behavior, he saw it as the ideal city. Compare this proverb to verse 2: "Every way of a man is right in his own eyes..." The proud wicked believe they are acting in accord to what is right in their own eyes which see by the lamp of haughtiness and pride.
All the more then humble yourself before the Lord. The Christian, too, is guilty of pride when he views his neighbor with haughty eyes, like the Pharisee looked upon the publican. We are easily proud that we see what our unbelieving neighbors do not. We act with great surprise that they do not see what we do. Why can't they understand the gospel? Why can't they know what is right from wrong? The answer is that they are no different from us. Without the work of the Holy Spirit in our hearts providing the lamp of God's truth, we would not "get it" either. And even with the Spirit within us, we still see too much with distortion out of our own pride. Indeed, we have less excuse than our unbelieving neighbor for our pride.