Our Lord expresses His meaning in the words, Ye are of this world, i. e. ye are sinners. All of us are born in sin; all have added by our actions to the sin in which we were born. The misery of the Jews then was, not that they had sin, but that they would die in their sin: I said therefore unto you, that ye shall die in your sin. Amongst the multitude, however, who heard our Lord, there were some who were about to believe; whereas this most severe sentence had gone forth against all: Ye shall die in your sin; to the destruction of all hope even in those who should hereafter believe. So His next words recall the latter to hope: For if ye believe not that I am He, ye shall die in your sin: therefore if ye believe that I am He, ye shall not die in your sin.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Tract. xxxviii. 6