Holiness is what God is. But since no one can define God, who can define Holy. Instead we are given 'Light' which can be defined since we have natural light. To fully understand 'Light' the symbolism we must first fully understand 'Light' the symbol. If you walk into a dark room that you are not fully acquainted with you will not see anything or know anything about what the room looks like or what was in it or anything about the room. You would in fact be completely ignorant about anything regarding the room. But if you hit the light switch and the light came on darkness would immediately dissipate before the light. You would then know all you needed to know about that room. "The light shines in the darkness, but the darkness has not understood it."[John 1:5] As we can see by this passage darkness cannot overcome light but light overcomes darkness. So we have the symbolism: Light is understanding and knowingness and darkness is ignorance and unknowingness. When we apply this in the context of God and His Word we see clearly that one leads to life (united with God) and the other to death (separated from God). For God Himself is life and if we are to be children of life then we must walk in His light which is His Holiness. All true believers are called Saints, which means separated onto God. But separated from what? Separated from the former existance of sin and death (darkness, ingnorance, fear, lust) to a new life of Love, Joy, Peace in the Holy Spirit. This is to my Father's glory, that you bear much fruit, showing yourselves to be my disciples.[John 15:8] Two things happen here: 1. bearing fruit qualifies you as Jesus' disciple and that in itself glorifies the father. But for a tree to bear fruit and much fruit it must have light.

Put your trust in the light while you have it, so that you may become sons of light." [John 12:36a]

[1 Thessalonians 5:5] You are all sons of the light and sons of the day. We do not belong to the night or to the darkness.

[1 John 1:5-10] NIV Walking in the light
This is the message we have heard from him and declare to you: God is light; in him there is no darkness at all. If we claim to have fellowship with him yet walk in the darkness, we lie and do not live by the truth. But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all sin. If we claim to be without sin, we deceive ourselves and the truth is not in us. If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives. [Rom. 12:14-21]