What does John 8:21-24 mean?

21 Then said Jesus again unto them, I go my way, and ye shall seek me, and shall die in your sins: whither I go, ye cannot come. 22 Then said the Jews, Will he kill himself? because he saith, Whither I go, ye cannot come. 23 And he said unto them, Ye are from beneath; I am from above: ye are of this world; I am not of this world. 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. (John 8:21-24 KJV)

William Burkitt’s Commentary

Observe here, A dreadful threatening denounced by Christ against the obstinate and unbelieving Jews. Ye shall die in your sins; that is, in the guilt of your sins, under the power, and undergoing the punishment of your sins:

Lord! what a sad word is this, Ye shall die in your sins. O better is it a thousand times to die in a ditch; for they that die in their sins, shall rise in their sins and stand before Christ in their sins; such as lie down in sin in the grave, shall have sin lie down with them in hell to all eternity. The sins of believers go to the grave before them; sin dieth while they live; but the sins of unbelievers go to the grave with them. While they live they are dead in sin: and by sin they fall into death; from which there is no recovery unto life.

Observe, 2. The grand sin for which this great punishment is threatened, and that is the sin of unbelief: If ye believe not that I am he, ye shall die in your sins.

Plainly intimating, that, of all sin, infidelity or unbelief is the grand damning sin under the gospel. The devil hath as great an advantage upon men, by making them strong in unbelief, as God hath by making his people strong in faith? Unbelief renders a sinner’s case desperate and incurable; it doth not only procure damnation, but no damnation like it.