A light is to show you the way in the darkness. If you don't have the light, you're in the dark.
Romans 10:1717 So then faith cometh by hearing, and hearing by the word of God.
2 Timothy 3:16-1716 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
17 That the man of God may be perfect, thoroughly furnished unto all good works.