"48 The Jews answered him, “Are we not right in saying that you are a Samaritan and have a demon?” 49 Jesus answered, “I do not have a demon, but I honour my Father, and you dishonour me. 50 Yet I do not seek my own glory; there is One who seeks it, and he is the judge. 51 Truly, truly, I say to you, if anyone keeps my word, he will never see death.” 52 The Jews said to him, “Now we know that you have a demon! Abraham died, as did the prophets, yet you say, ‘If anyone keeps my word, he will never taste death.’53 Are you greater than our father Abraham, who died? And the prophets died! Who do you make yourself out to be?” 54 Jesus answered, “If I glorify myself, my glory is nothing. It is my Father who glorifies me, of whom you say, ‘He is our God.’ 55 But you have not known him. I know him. If I were to say that I do not know him, I would be a liar like you, but I do know him and I keep his word. 56 Your father Abraham rejoiced that he would see my day. He saw it and was glad.” 57 So the Jews said to him, “You are not yet fifty years old, and have you seen Abraham?”"
John 8:48-57
The accusation of demon possession levelled against Jesus in these verses represents the 'last-ditch' stand the Pharisees can make. And they take refuge in it, with something like desperation. One thing is clear: the Jews were in no doubt as to the kind of claim Jesus was making for Himself. They knew He was claiming Deity; and since this to them was unthinkable, the only possible alternative must be that he had a devil. Only one who was either devil possessed or the Messiah could dare to speak as He does in 51. This is what lies behind the contemptuous question they ask in 53, 'Art thou greater than our father Abraham?' To this Jesus answers two things; firstly, that 'Abraham rejoiced to see my day: and he saw it and was glad'. This categorically claims His own pre-xistence. Jesus means and implies that Abraham's faith looked forward to His own coming, and indeed rested upon that coming: and by implication He indicated that the faith of all the old dispensation was faith in the promise of His coming. Secondly, He uttered perhaps the most profound of all His statements, 'Before Abraham was, I am'. These words not only serve to reinforce the earlier claim in 56, making even more explicit His pre-existence, but also in the use of the sacred 'I am' emphasises His eternal pre-existence and His essential Deity. The assumption of the divine Name of the Old Testament could lead only to worship and adoration on the part of those who believed in Him, and the assumption of blasphemy on the part of those who did not. It was on this ground that they took up stones to throw at Him (59).