John 8:46-50 comments: He that is of God heareth God's words...

46 ¶  Which of you convinceth me of sin? And if I say the truth, why do ye not believe me? 47  He that is of God heareth God’s words: ye therefore hear them not, because ye are not of God. 48  Then answered the Jews, and said unto him, Say we not well that thou art a Samaritan, and hast a devil? 49  Jesus answered, I have not a devil; but I honour my Father, and ye do dishonour me. 50  And I seek not mine own glory: there is one that seeketh and judgeth.

Convince and convict and reprove and refute have a similar meaning. See Titus 1:9 and Jude 1:15.

If His listeners had any part in God they would have believed Jesus’ words. But, the stiff-necked unbeliever cannot hear because He is not of God. This is the reason why many people are so adamantly opposed to Christianity who don’t seem to be offended by any other religion. When you take out the ignorant behavior and paranoia of certain Christians the main reason why people get so incensed when you talk about your faith is because they have no part in their Creator nor do they care to have any.

The conversation now goes beyond the shallow believers He was provoking to the Jews who were listening, as well, who are even more incensed at His words. The chorus joins in with an insult that Jesus is a Samaritan, which is an insult as the Jews hated Samaritans, and that He has a devil, which was the unforgiveable sin. As the three parts of God work in the world and the Holy Ghost points people toward Christ to state that Christ was possessed by or doing the work of Satan was to blaspheme the Holy Ghost which was the unpardonable sin.

Mark 3:22 ¶  And the scribes which came down from Jerusalem said, He hath Beelzebub, and by the prince of the devils casteth he out devils. 23  And he called them unto him, and said unto them in parables, How can Satan cast out Satan? 24  And if a kingdom be divided against itself, that kingdom cannot stand. 25  And if a house be divided against itself, that house cannot stand. 26  And if Satan rise up against himself, and be divided, he cannot stand, but hath an end. 27  No man can enter into a strong man’s house, and spoil his goods, except he will first bind the strong man; and then he will spoil his house. 28  Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith soever they shall blaspheme: 29  But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation: 30  Because they said, He hath an unclean spirit.

Those who would say that would never come to repentance. Their opportunity for salvation was cut off. From that point on they would be object lessons in the wickedness of lost humanity. Any person who believes in the spiritual world who claims that Jesus of Nazareth was a man possessed by an unclean spirit, a devil, shall not receive eternal life by virtue of his profession. Any atheist, perhaps, by extension, who declares that, based on Jesus’ claims about Himself, He was an evil man, a liar, and a charlatan has also sealed his fate by blaspheming the work of the Holy Ghost in this world of men and women. Who can say?

Jesus denies He has a devil but that He honors His Father while they dishonor Him. He is seeking the Father’s glory. The Father is the ultimate judge of mankind although that authority is invested in the Son (John 5:22). In the next passage Jesus will declare that He is God in no uncertain terms.