"Therefore I said to you that you will die in your sins; for unless you believe that I am He, you will die in your sins" (John 8:24).
Belief in Christ is essential for salvation. But the belief that Jesus mentions here is more than just a belief that he existed, came to earth, died for our sins, rose again from the dead, and ascended back into heaven. Yes, we must believe those things about Jesus. But if that is the extent of our belief, we will die in our sins.
If you read this verse in your Bible, where Jesus says, "unless you believe that I am He," the word "He" is probably in italics, differentiating it from the rest of the words. The reason for this is that the word was added by the translators. It is not in the original text. What Jesus actually said is, "unless you believe that I am, you will die in your sins." This clearly points back to Moses' conversation with God when God called Himself the "I AM" (Exodus 3:14). This is also not the only time Jesus used this phrase in this way (John 8:58).
So what Jesus is actually teaching here is that unless we believe that He is God, we will die in our sins. That means we must recognize Him as our God and humbly submit to His will in faithful obedience (Hebrews 5:9). If we truly believe in Christ, that He is "King of kings and Lord of lords" (Revelation 19:16), we will do what He has instructed us to do.
"Faith without works is dead" (James 2:26), and a dead faith will ultimately result in us dying in our sins.