God is light: This means that God is completely pure, good, and true. When Jesus Christ lived on earth, this light shone through him to everyone he met. His life exposed the sin in people’s hearts, because his words and actions showed God’s perfect standard. At the same time, his light also helped people understand what God is really like—his goodness, his mercy, and his desire for people to walk in truth (see John 1:4–5, 9; 3:19–21; 8:12; 9:5; 12:35–36, 46).
In the writings of John, “light” stands for God’s holiness and his clear revelation of what is right. “Darkness” refers to false teaching and to living without self-control or obedience to God. These two ways of life cannot mix. People who walk in the light live in the truth of God. People who walk in darkness follow what is false and harmful (1 John 1:6).