From: John 8:12-20
Jesus, the Light of the World
 Again Jesus spoke to them saying, "I am the light of the world; he who follows Me will not walk in darkness, but will have the light of life."  The Phariees then said to Him, "You are bearing witness to Yourself; Your testimony is not true."  Jesus answered, "Even if I do bear witness to Myself, My testimony is true, for I know whence I have come and whither I am going, but you do not know whence I have come or whither I am going.  You judge according to the flesh, I judge no one.  Yet even if I do judge, My judgment is true, for it is not I alone that judge, but I and He who sent Me.  In your law it is written that the testimony of two men is true;  I bear witness to Myself, and the Father who sent Me bears witness to Me."  They said to Him therefore, "Where is Your Father?" Jesus answered, "You know neither Me nor My Father; if you knew Me, you would know My Father also."  These words He spoke in the treasury, as He taught in the temple; but no one arrested Him, because His hour had not yet come.
12. This is the beginning of another dispute between Jesus and the Pharisees. The scene is the precincts of the temple--to be more precise, what was called he "court of the women"; this came before the court of the people, which in turn came before the court of the priests, which contained the altar of holocausts (cf. note to Luke 1:21).
It is still the feast of Tabernacles (cf. John 7:2); and it was the custom on the first night to fill the court of the women with the bright light of huge lamps which lit up the sky. This brought to mind the bright cloud of God's presence which guided the Israelites through the wilderness during the Exodus. It was probably during this feast that Jesus spoke of Himself as "the Light". In any event, the image of light is often found in the Old Testament to designate the Messiah: the prophet Isaiah predicted that a great light would shine for the people who walked in darkness, beginning with the tribes of the North (Isaiah 9:1-6; cf. Matthew 4:15-16) and that the Messiah would not only be the King of Israel but the light of the nations (Isaiah 42:6; 49:6); and David spoke of God as a light enlightening the soul of the righteous man and giving him strength (Psalm 27:1). This image, therefore, was well understood during Jesus' time: Zechariah uses it (Luke 1:78), as does Simeon (Luke 2:30-32), to show his joy on seeing the ancient prophecies fulfilled.
Our Lord applies this image to Himself in two ways: He is the light which enlightens our minds, for He is the fullness of divine Revelation (cf. John 1:9, 18); and He is also the light which enlightens our hearts to enable us to accept this Revelation and live according to it (cf. John 1:4-5). This is why Jesus asks them to follow Him and become sons of light (cf. John 12:36), although He knows that many will reject this light because they do not want their evil deeds to be uncovered (cf. John 3:20).
"See how the words of the Lord accord with the truth of the Psalm: 'With Thee is the fountain of life; in Thy light do we see light' (Psalm 36:10). The psalmist connects light with the source of life, and the Lord speaks of a 'light of life'. When we are thirsty, we look for a fountain; when we are in darkness we look for light. [...] Not so with God: He is light and fountain. He who shines for you to enable you to see, flows for you to enable you to drink" (St. Augustine, "In Ioann. Evang., 34, 6).
13-18. The Pharisees try to dilute the force of Jesus' arguments: they make out that He has only His own word to go on and no one can bear witness on his own behalf: so what He says has no validity.
In a similar situation (cf. John 5:31ff) Jesus had cited four witnesses to support Him -- John the Baptist's teaching, the miracles He Himself performed, the words His Father spoke when He was baptized in the Jordan, and Sacred Scripture. Here Jesus affirms the validity of His own testimony (verse 4) on the grounds that He is one with the Father. This is the same as saying that His is more than human testimony. "He speaks to tell them that He comes from God, that He is God, and that He is the Son of God, but He does not say so openly, because He always connects humility with profundity. God deserves that we should believe in Him" (St. John Chrysostom, "Hom. on St. John", 51).
19. The Pharisees, who did not want to admit Jesus' divine origin, now ask Him for proof that what He says is true. Their question is insidious and malicious, for they do not think He can show them the Father.
Knowing Jesus, that is, believing in Him and accepting the mystery of His divinity, means knowing the Father. John 12:44-45 repeats the same teaching in other words. And Jesus is saying the same when He reproaches Philip: "Have I been with you so long and you do not know Me, Philip? He who has seen Me has seen the Father" (John 14:9). Jesus is the visible manifestation of the invisible God, the ultimate, definitive revelation of God to men (cf. Hebrews 1:1-3). Jesus Christ "by the total fact of His presence and self-manifestation--by words and works, signs and miracles, but above all by His death and glorious resurrection from the dead, and finally by sending the Spirit of truth [...] revealed that God was with us, to deliver us from the darkness of sin and death, and to raise us up to eternal life" (Vatican II, "Dei Verbum", 4).
20. "The treasury", where money for the poor was collected, was located in the women's courtyard. For more information see the note on Luke 21:1-4.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.