I said therefore 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, WEB)
Who is the I am he that Jesus refers to here? Jesus is saying He was sent from the Father as God, Jesus is creator of everything.
Jesus was crucified for our sins, buried and rose the third day, so that if we believe in Him we may have eternal life.