Proverbs 21:2 says, "All a man's ways seem right to him, but the LORD evaluates the motives."
We often think we are great judges of character--especially our own character. They may think they know me, but they don't know me... not like I know me. I'm a really good person. I have evaluated myself, and look, see I am very good.
Left to our own devices, we are not great judges of our selves at all. Oh sure, we are able to evaluate ourselves honestly to a degree. But, wholly, completely? No. Much of our sins are hidden in darkness (and many are laid open for others to see). Consider the entire spectrum of sin, and consider the entire spectrum of light. Much of light is not seen by the naked eye so to is man's sin. Though we think we are great at seeing all the light, we really aren't good at all. We miss so much.
Consider how little of the light spectrum we can see. Now, sin is not light... Jesus is the light. But it is by the light that our sins are exposed and dealt with.
Jesus said, "And this is the judgment: the light has come into the world, and people loved the darkness rather than the light because their works were evil. For everyone who does wicked things hates the light and does not come to the light, lest his works should be exposed." (John 3:19-20)
Most often, this saying of Jesus is simply understood as there are parts hidden in darkness; willingly concealed or otherwise, but sins hidden that are in shadows we aren't willing (or maybe even able) to see. I think that is a fine understand of what Jesus is saying. However, I believe it is also understood in considering the spectrum of light that exists beyond our scope of vision.
With Jesus, He will reveal things to us (by the light) that we never saw before. Even then, though, our minds can only fathom so much at a time. He reveals it little by little over our entire life, and He is faithful through it all. Our only hope for true exposure of our sin and consequently forgiveness, is to step into the light--the One who covers the entire spectrum seen and unseen--in order to be healed.
It is often put forth that "No man (mankind) can judge me, only God can do that!" In some regard, I say Amen! You (I) cannot even judge yourself! Yet to truly grasp the depth of our own depravity, is to grasp that we are as equally unqualified to judge the depths of our own motives as any other man would be. Only God can judge me (truly, wholly, completely), and He will. If you haven't stepped into the light, however, then we shouldn't count on that fact working in your favor.
So, what then? If we cannot even know the depravity of our own hearts such that we can stand firm on our own righteousness, how can we hope to stand before God who knows the motives of our hearts? How can we ever hope to justify ourselves and make ourselves pure? We can't.
When God judges sin--all sin--in the most secret regions of your heart, how can a man hope to be ready? There is coming a day when God will judge the secrets of our hearts (Romans 2:16); secrets even to us. Secrets that if revealed to you--fully the whole depth of depravity--it would leave us as an irreconcilable heap of pity.
SO, JESUS.
We cannot deal with our own blindness to our own sin, on our own. We cannot see the entire spectrum of our sin without the help of the light, or hope to have it reconciled. With man, this is impossible; but with God, all things are possible (Matthew 19:26). He is our only hope to have our sins--both sins glaringly obvious or secretly concealed--paid for completely above and beyond what we could have ever understood on our own.
Again Jesus spoke to them, saying, “I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.” (John 8:12)