Light and darkness make up one of the conspicuous dualisms that are found in John’s Gospel. The source of such dualism in John is not Gnosticism or Greek philosophy, but the concept of light and darkness in the Hebrew Bible. Therefore, in order to understand John’s concept of light and darkness, we need to consider the Old Testament background to this idea.
Consistent with the characterization of light and darkness in many cultures, in the Old Testament light is a positive concept, whereas darkness is primarily negative (Isa 5:20). In Gen 1, darkness is associated with disorder and emptiness. The default state of the world is darkness, but the word of God brings light into the world (Gen 1:3; see also Isa 42:16). Darkness can be associated with the presence of God in the sense that the thickness of his glory cloud can prevent light from penetrating (Exod 14:20; 20:21; Deut 4:11; 5:22–23; 1 Kgs 8:12; Ps 18:9, 11; 97:2), and in the sense that God is the creator of (physical and metaphorical) darkness (Isa 45:7; Amos 4:13); but overall Yahweh is a God who dwells in glorious light (Exod 27:20; Ps 104:1–2; Ezek 1:27–28). He is the light of the righteous (Ps 27:1). His light gives light to his people (Ps 36:9; see also Ps 56:13; 97:11). Light shines from his face (Ps 44:3; 89:15). To the righteous, his word “is a lamp unto my feet, and a light unto my path” (Ps 119:105; see also Ps 119:130; Prov 6:23).
Darkness is usually a sign of God’s judgment (Exod 10:21–23; Ps 105:28; Ezek 32:8; Joel 2:2, 31; Amos 5:18, 20; Nah 1:8; Zeph 1:15). The covenant curse of military defeat for Israel will see darkness covering the land (Isa 5:30; 8:22). The exile is pictured as a time of darkness (Jer 13:16). Darkness is also associated with death (Ps 107:10, 14; Prov 20:20). It is the ultimate abode of the wicked (1 Sam 2:9). There is no light in Sheol, the place of the dead (Ps 49:19). From the ethical perspective of the Old Testament, the problem with darkness is that it does not allow you to see where you are going. Darkness is dangerous. You cannot see the spiritual obstacles that would bring you down, which means that you can easily end up stumbling off the pathway that leads to life (Prov 4:19; Isa 59:10; Jer 23:12). To forsake the paths of uprightness is to walk in darkness (Prov 2:13). Evildoers hide in the darkness (Job 34:22). The righteous can also experience darkness (Isa 50:10; 59:9; Lam 3:2), but in the end light will shine upon the upright (Ps 112:4). Yahweh is a lamp who shines his light into the darkness experienced by the righteous (2 Sam 22:29; see also Mic 7:8–9). Repentance will result in the light dawning upon the darkness of Israel such that even her gloom will be as bright as noon (Isa 58:8, 10).
The eschatological coming of Yahweh is pictured in the Old Testament as the light of the glory of God that comes to push back and to overcome the darkness of this world. Yahweh will arise, and his glory will shine upon Israel, and be a beacon that will attract the nations (Isa 60:1–3). Emmanuel, the child of the young (virgin) woman (Isa 7:14), who is “Mighty God” (Isa 9:6), will come as “a great light” shining in “Galilee of the Gentiles” (Isa 9:1–2); and the Suffering Servant will be “a light for the Gentiles” (Isa 42:6; see also Isa 49:6; 51:4–5). In this way, the day of salvation will bring light to the blind (Isa 29:18; 42:7); the prisoners will be released from darkness (Isa 49:9); and the glory of Yahweh will become an everlasting light, so bright that the sun will be made redundant, its brilliance being eternally eclipsed by the utter magnificence of the glory of God (Isa 60:19–20).