In the Greek it is only, if ye believe not that I am. Some refer this to Christ's Divine nature; ( I am, is the name of God, Exodus 3:14); but others rather think that Christ here speaketh of himself as the Messiah and Mediator, and so the object of people's faith; and he out of whom there is no salvation: the latter indeed includes the former; for cursed is he that trusteth in man, and maketh flesh his arm, Jeremiah 17:5. The text plainly holds forth an impossibility of salvation for those who, under the revelations of the gospel, receive not and believe not in Christ as Mediator.
Related Commentaries of John 8:24
John 8:24
24 I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am he, ye shall die in your sins.