John 8:21 - Joseph Benson’s Commentary on the Old and New Testaments

Then said Jesus again Probably in the same place where the preceding discourse was pronounced; and still confiding in the protection of Divine Providence; I go my way That is, I shall speedily go away from among you; and ye shall seek me Shall inquire after the Messiah; and shall die in your sins Impenitent and unbelieving, and therefore unpardoned. Or, ye shall die, suffering the punishment of your sins: you shall perish for your unbelief and rejection of me, by a singular stroke of divine vengeance. The threatening, thus explained, conveys a prediction of the destruction of their city and state, in which probably some, that were now our Lord's hearers, afterward perished. Whither I go ye cannot come Either to molest me, or to secure yourselves. Though you should be ever so desirous of being admitted into my presence, the favour will not be granted you. He repeats what he had said to them in a former discourse, (see on John 7:33-34,) that it might make the deeper impression upon them. “He meant, that after his ascension into heaven, when the Roman armies were spreading desolation and death in every corner of the land, they would earnestly desire the coming of the Messiah, in expectation of deliverance, but should perish for their sins, and under the guilt of them, without any Saviour whatsoever, and be excluded for ever from heaven.” Some think, that in saying this, our Lord opposed a common error of the Jews, who imagined, that by death they made atonement for all their sins.