The Pharisees challenged him, “Here you are, appearing as your own witness; your testimony is not valid.”
The Pharisees stand in opposition to Jesus, but they do not address His statement; instead they characteristically raise a legal technicality.
“not true” (NIV) = “not true” (KJV) = does not mean “false” but “not valid” or having no legal worth. According to the Mishnah, “No man can give witness for himself” (Ketub. 11. 9).
The Pharisees did not wish to enjoy the Light from God, but instead to extinguish its revealing blaze. This is a reminder of (John 1:5). The Pharisees of Jesus’ time and men today say that they do not see Jesus as being the light of the world and that the evidence does not support His claim; but they didn’t create that light of which He speaks and when they refute its existence they do so only to their own satisfaction. Light is still light, and their rejection of its existence does not condemn the light, but them. As Morris states, “light establishes its claim. It does so by shining. Light must always be accepted for itself, and that notwithstanding the objections of the blind.” (439)
John 1:5 The light shines in the darkness, but the darkness has not understood it.