"12 Again Jesus spoke to them, saying, “I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life.” 13 So the Pharisees said to him, “You are bearing witness about yourself; your testimony is not true.” 14 Jesus answered, “Even if I do bear witness about myself, my testimony is true, for I know where I came from and where I am going, but you do not know where I come from or where I am going. 15 You judge according to the flesh; I judge no one. 16 Yet even if I do judge, my judgement is true, for it is not I alone who judge, but I and the Father who sent me. 17 In your Law it is written that the testimony of two people is true.18 I am the one who bears witness about myself, and the Father who sent me bears witness about me.” 19 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.” 20 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."
John 8:12-20
This was the failure and blindness of the Pharisees: they could not tell whence He came and whither He was going. They were blind to His identity, knowing Him only after the flesh (15), and what follows from 16 onwards serves to emphasise this, and the fact that there was really no point of contact between them. Jesus was not alone (16) - this is the point made in 5:31ff - for the Father bore witness to Him also, and therefore there is a twofold witness to Him, which fulfills the rabbinical law about two witnesses being required (17, 18). But they ask, 'Where is thy father?' (19) They did not ask, 'Who is thy father?' - that would have shown that there was some gleam of dawning light in their hearts. But they spoke with contempt, thinking his father to be Joseph the carpenter. Not Jesus the mere historical personage, but Jesus the Son of God - this is the point they did not, would not, see. But to see no more in Jesus than a human, historical personage, is not to see Him at all in any significant, spiritual sense. The gulf between them and Jesus is complete.