This is the message which we have heard from him and announce to you, that God is light, and in him is no darkness at all.
The figure of light that John used to describe God emphasizes His ability to reveal and His ability to deal with what the light of His holiness reveals (cf. John 1:4-5; John 1:7-9; John 3:19-21; John 8:12; John 9:5; John 12:35-36; John 12:46; Revelation 21:23). John elsewhere described God as spirit (John 4:24) and as love (1 John 4:8). All three comparisons of God stress his immateriality and essence. God exposes and condemns sin (called "darkness" in John 1:5; John 3:19; John 12:35 [twice], and in 1 John 1:5-6; 1 John 2:8-9; 1 John 2:11 [twice]). The light figure emphasizes these qualities in God: His splendor and glory, His truthfulness, His purity, His self-communicative nature (cf. Psalms 27:1; Psalms 36:9; Isaiah 49:6; John 1:9), His empowering activity (cf. John 8:12; John 12:35; Ephesians 5:8-14), and His right to demand (cf. John 3:19-21). The light-darkness motif was common in both the Hellenistic and Jewish thought life of John’s day and culture. [Note: Dodd, pp. 18-19; John R. W. Stott, The Epistles of John, p. 70; Theodor H. Gaster, The Dead Sea Scriptures, pp. 46, 49-51.] For John these concepts were mainly ethical (cf. Ephesians 5:8-14).