‘Jesus answered, ‘If I glorify myself, my glory means nothing. It is my Father who glorifies me, of whom you say that he is your God. But you have not known him. But I know him, and if I said that I did not know him I would be a liar like you. But I do know him, and keep his word'.
Jesus did not directly answer their jibe. Rather He diffused their argument by disclaiming any desire to glorify Himself. They claimed that His Father was their God. Well, let them consider this. It was the One Whom they claimed as their God Who was the One Who would glorify Jesus, and indeed was already doing so through His wonderful works. Thus by not recognising Him they were proving that they did not actually know the Father. In contrast with them Jesus did know Him and He kept His word faithfully, as their own failure to convict Him of sin earlier established. To suggest any other position would make Him a liar like them. There was obviously now no holding back. Both had made their positions clear.
‘You have not known Him --- but I know Him.' The first ‘know' is ginosko, to know by experience, the second is oida, to know by understanding. This may be an intentional contrast, stressing that whilst they had not even truly experienced the Father, Jesus had not only experienced His Father but knew His mind. He knew Him through and through (compare Matthew 11:25-27).
At this point Jesus, in full awareness of what He is doing, now makes His past comments absolutely clear. They had asked Him whether He was greater than Abraham. Well, He would now tell them the truth.