What does John 8:49 mean?

Jesus makes an important distinction here, which further shows the difference between Him and His critics. Everything Jesus did in His earthly ministry was intended to glorify God the Father. And, Jesus always pointed His mission, His words, and all of the credit for those accomplishments to God (John 8:50). The Pharisees, like other religious leaders of that era, were more interested in their own power and prestige than in the truth (Matthew 20:25; Luke 11:43; Matthew 23:6). Since Jesus' message conflicts with what they want to believe, they refuse to understand it (John 7:17). This is why Jesus was comfortable in saying that they were, spiritually, the children of the devil, not of Abraham (John 8:44).

Recently, this same hostile crowd has resorted to petty insults. In the prior verse, these critics have insulted Jesus' birth and accused Him of being insane. This only goes to prove the point Jesus has made over and over: those who reject the One sent by God are also rejecting God (John 3:36). To dishonor Jesus is to spit in the face of God the Father.