Because Jesus is God in flesh, his testimony is self-authenticating and his teaching is revelatory

John 8:12–20

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 judgment 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.