Jesus spoke this right before he raised Lazarus from the dead. But He was also speaking prophetically about His own resurrection; for whoever believes in Him shall never die but will live eternally. Jesus wasn’t talking about physical death but spiritual death, which is being separated from God eternally.

Romans 10:9 says, “That if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved.”

Believing God raised Jesus from the dead is important, because Jesus was the first born or the first born again among many.

Romans 8:29 says, “For those God foreknew he also predestined to be conformed to the image of his Son, that he might be the firstborn among many brothers and sisters.”

Because the first Adam died spiritually through disobedience to God, Jesus, the second Adam, defeated death through His obedience to God.

I Corinthians 15:42-45 says, “So it is with the resurrection of the dead. [The body] that is sown perishable and decays, but [the body] that is resurrected is imperishable (immune to decay, immortal). It is sown in dishonor and humiliation; it is raised in honor and glory. It is sown in infirmity and weakness; it is resurrected in strength and endued with power. It is sown a natural (physical) body; it is raised a supernatural (a spiritual) body. [As surely as] there is a physical body, there is also a spiritual body .Thus it is written, The first man Adam became a living being (an individual personality); the last Adam (Christ) became a life-giving Spirit [restoring the dead to life].”

Hebrews 2:9-14 says, “But we are able to see Jesus, Who was ranked lower than the angels for a little while, crowned with glory and honor because of His having suffered death, in order that by the grace (unmerited favor) of God [to us sinners] He might experience death for every individual person. 14Since, therefore, [these His] children share in flesh and blood [in the physical nature of human beings], He [Himself] in a similar manner partook of the same [nature], that by [going through] death He might bring to nought and make of no effect him who had the power of death—that is, the devil—“

Colossians 2:12-13 says, “Buried with Him in baptism, in which you also were raised with Him through faith in the working of God, who raised Him from the dead. 13 And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses."

I was made alive with Christ through His death, burial, and resurrection,