bible.com/bible/100/jhn.8.12.NASB1995

Taken from John MacArthur Study Bible

The phrase highlights Jesus’ role as Messiah and Son of God (Ps 27:1; Mal 4:2). The OT indicates that the coming age of Messiah would be a time when the Lord would be a light for His people (Is 60:19–22; cf. Rev 21:23, 24) as well as for the whole earth (Is 42:6; 49:6). Zechariah 14:5b–8 has an emphasis on God as the light of the world who gives living waters to His people.