John 8 begins with the narrative of the woman caught in adultery. This section, while an authentic eyewitness account of the Gospel, was probably not written by John, since early manuscripts attached it to different gospels or different parts of John, but it was too important to be left out of the Gospel altogether.
Jesus proclaims that He is the Light of the world. Darkness is used to denote that which is not of God throughout the Bible. Psalms 27, 36, 119, Numbers 6, and Isaiah 49 correlate light with God and God's gift of life. The Pharisees object that Jesus has not confirmed His testimony by another witness, a legal procedure. Jesus states that His testimony is confirmed even if He states it Himself, since He does not judge, but rather the Father.
Jesus then speaks of His death, but the Pharisees do not understand. Jesus tells them that they will understand when He is lifted up, which refers to His crucifixion.