Concise Bible Dictionary:

Besides the references to physical light as existing distinct from the sun, and then emanating from the sun as the great light-bearer, the term is mainly used in scripture in a moral sense. Light from God is His word revealing Himself, and not only making manifest the dangers here, but acting as a lamp in showing the true path (Psa. 119:105). The Psalmist asked Jehovah to lift upon him the light of His countenance (Psa. 4:6), and declared that Jehovah Himself was his light (Psa. 27:1). As natural light brings vigor and health to the body, so the light of God gives cheerfulness and strength to the soul.
“God is light,” and the Lord Jesus came to the earth as the true light which lighteth every man. He not only exposed all the evil in the world and all the false pretensions of the leaders of Israel; but “the life was the light of men” (John 1:4; John 8:12). Christians are “light in the Lord,” and are exhorted to walk as “children of light” (Eph. 5:8; 1 Thess. 5:5). In the midst of darkness they are set to shine as lights in the world (Phil. 2:15). A grave responsibility rests upon them lest they should not have the heavenly luster that would characterize them as having in their hearts the light of the glory of the Lord. If the light in the Christian become darkness by his not walking in the reality of it, how great is that darkness! (Matt. 6:23).
It has been very properly said that light is appropriately descriptive of God; for light, invisible in itself, manifests everything. Christians, as we have seen, are “light in the Lord,” and thus convict the unfruitful works of darkness; but here we may notice that it is not said of them, as of God, that they are “love,” for love is the sovereign, spring of activity in God.

From Manners and Customs of the Bible:

Job 18:5-6. Yea, the light of the wicked shall be put out, and the spark of his fire shall not shine. The light shall be dark in his tabernacle, and his candle shall be put out with him.
To the susceptible mind of the Oriental, light is an object of desire, and darkness something to be greatly dreaded. The lamp is usually kept burning in the house all night; and its light is used as an emblem of prosperity, and the extinguishment of it as an emblem of a great calamity. Thus Job speaks of the days of his prosperity when the candle of the Lord shone upon his head (Job 29:3). David says, “Thou wilt light my candle: the Lord my God will enlighten my darkness” (Psa. 18:28). On the other hand, we find Job saying, as expressive of great affliction: “How oft is the candle of the wicked put out” (Job 21:17). Solomon says, “Whoso curseth his father or his mother, his lamp shall be put out in obscure darkness” (Prov. 20:20). “The candle of the wicked shall be put out” (Prov. 24:20).
The Saviour on two occasions refers to this Oriental dread of darkness where he represents the punishment of the wicked under the figure of “outer darkness.” See Matthew 8:12; 22:13. Both ideas are blended in Proverbs 13:9: “The light of the righteous rejoiceth: but the lamp of the wicked shall be put out.”
See also Jeremiah 25:10.

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