What does John 8:19 mean?
In defending His claim to be "the light of the world" (John 8:12), Jesus claimed to have equal judgment to God, whom He called His "Father." This was part of Jesus' argument that, as the only man who had actually seen the heavenly things He was speaking of, it was acceptable for Him to "testify" about Himself (John 8:13–18). In addition, the miracles He performed were proof—by the Pharisees' own logic (John 3:1–2)—that His mission was approved by God. In response, the Pharisees have diverted the conversation to question what Jesus means when He speaks of His "father."This terminology would have been both confusing and controversial for the Pharisees. They did not think of God in terms of a Father-Son-Holy Spirit Trinity, and certainly did not believe that Jesus was the Son of God. The question asked here might also be a subtle dig at Jesus. One of the insults these men will throw at Him later is an allusion to His birth, hinting that His lack of an earthly father was, in fact, because He was an illegitimate child.
Here, Jesus continues to directly castigate these critics. Jewish people, especially those highly educated in the law of Moses, prided themselves on "knowing" God. For Jesus to claim that they do not know God is a cutting remark. Beyond that, Jesus adds to His claims of divinity. Those who know Jesus Christ know God (John 1:14), and those who reject Jesus Christ are turning away from God (John 3:36).