The power of this light is the self-knowledge it renders to man. When a man gets into this light, it reveals to him his real condition. Many believers are very self-vindicating, self-satisfied, and full of self-pride. In this condition no human words, explanation, exhortation, warning, or reproof can make them see their own fallen state. Only when God gives grace and shines His light upon them through the Holy Spirit will this kind of person realize how corrupt, fallen, and hypocritical they are. When the light of God comes, everything changes color. In the light of God, everything shows its true color.
Actually, no man can be saved without being shined upon by God. No man can progress in the spiritual path and no man can have an effective work without being shined upon by God.
How can a sinner know that the Lord Jesus is the Savior? Surely not by argument. How can he know that he is a sinner? Surely not by reproof. No matter what method you use, whether arguing with the most logical words, debating with the most sufficient reason, or warning with the most stern words; none of these can make a sinner realize his own sins and see that Jesus is his Savior. I am not saying that all these methods are useless. They have their place. But they can only let people know mentally that they are sinners and that Jesus is the Savior. These methods can never cause them to see. Every sinner is blind, and this kind of blindness keeps him from seeing the true light of the gospel of God. The Holy Spirit opens the sinner’s eyes through the light of God, enabling him to see the light of God. Seeing is a special blessing in the New Testament. God reveals His Son in me. This is an experience common to every saved sinner. It is most futile to get people to "receive Christianity," "believe in Jesus," and "become a Christian" by some beautiful thought, reason, warm feeling, emotion, music, tears, or argument. The light of God, the light that God emanates through the Holy Spirit, is the first indispensable element. The basic need is that a sinner must see his own condition and see the glory of Jesus. Getting him to shed tears, repent, be fervent, confess, and have good feelings are all futile. Only seeing in the Holy Spirit can cause a sinner to truly believe and receive the Lord Jesus as Savior. This is because you can never believe in what you have not seen, and you can never receive what you do not see. Because you have seen from within, you believe. Only this kind of faith is unmovable. Only this will withstand trials.
The progress of the Christian life does not depend upon many exhortations, warnings, and teachings. It is not a matter of telling a believer to be fervent, to do his duty, to read more of the Bible, or to pray more. All these are secondary; they are not primary. The primary element is to see. Therefore, when Paul wrote the letter to the Ephesians, though he knew that they were very good in the Lord and were not like the Corinthians who were so fallen morally, the first thing which he prayed for them was that God might enlighten the eyes of their hearts through the Holy Spirit. The progress of the Christian life is due to receiving the light of God, which opens a Christian’s eyes and causes him to know the riches of the glory of God, and the greatness of the power of God that is given to him through the resurrection of Jesus Christ. If a Christian cannot see these things and does not know how rich these things are which he has received from God, then progress is an impossibility.
Anyone who is doing special work for God must be a person who has been shined upon by God. Only he who has been shined upon by God can judge his flesh. Only he who has judged his own flesh can be used by God. When the light of God comes, a believer is able to see how filthy he is because he has seen the holiness of God. He is able to know how unrighteous he is because he has seen the righteousness of God. He is able to know how corrupt he is because he has seen the glory of God. After a believer has known himself this way, he will be like one who is truly circumcised, not trusting in himself at all (not only not trusting, but deeply hating), but rather depending completely on the Spirit of God. Only this type of worker who is in the hands of God can be used by God. And only this type of worker can have the sight of God, seeing the plan of God and understanding the goal of God.
Because many people do not have the light of God, they consider themselves to be marvelous. Satan often cheats people by making them think that they have already obtained holiness and are sinless. Little do they realize that the reason they say this is because they do not have the light of God; hence, they do not know the corruption of the flesh. I am one who deeply believes in Christ being our life and that He can enable us to completely overcome sins. No Christian can excuse himself by saying that it is impossible for man to refrain from sin on this earth. But even if we are victorious, we cannot say that our flesh is not corrupted. There is a common error today: man either goes to one extreme or to the other. Some think that since they are corrupt, it is impossible for them not to sin. Others think that since they have received Christ to be their victory, sin is eradicated from within them, and therefore, they are no longer corrupt. Actually both of these are wrong. Truthfully, we are victorious in Christ, but we are corrupt in ourselves. A believer can have a life of complete victory over sin through Christ daily, and he can, at the same time, have the feeling every day that he is corrupt to the uttermost. The feeling of decadence and corruption cannot deter his victory because it is Christ overcoming in him and not himself. Likewise, his complete victory cannot remove from him the feeling of total corruption because the corruption of his flesh will not be changed in its nature by the deliverance of Christ.
Because so many have been deceived, thinking in their own small and dim light that they are so holy, sinless, and perfect in love, we need to see how many of the best and deepest saints in the Bible viewed themselves in the light of God.
(Self-Knowledge and God's Light, Chapter 1, by Watchman Nee)