Christ is not being inconsistent with the balance of the Holy Bible when he said that whoever believes in him would never see death, though all still commonly die physically speaking, and this is why:
The application of the sacrificial atonement of Christ effectively prohibits death from claiming anyone who has been made an object of that blood redemption. However, although the death of Christ legally procured or purchased the entire and whole man or woman who truly believes in him, that death is only applied partially, in that it only immediately redeems now the spiritual man/woman, and deliberately neglects to redeem that same person's physical man/woman, and so allows for a physical death to take place that would have not otherwise occurred. So, here we have a true and genuine believer in Christ who, (it would seem,) cannot die, and yet must die! Why?
"Now this I say, brethren, that flesh and blood cannot inherit the Kingdom of God; nor does corruption inherit incorruption." I Corinthians 15:50
Since Jesus the Messiah purchased his beloved bride with his priceless, matchless and incontestable life blood, he hasn't the least intention of seeing that dear bride unredeemed in any way, right down to the smallest hair upon her lovely head. Everything that Messiah has purchased...absolutely everything, must effectually be redeemed, or the death of that Messiah would have been in vain, an utter impossibility for the omniscient mind which designed the atonement. However, if Christ the Messiah applied the saving virtue of his sacrifice to any believer here on earth now, that person would then be legally exempted from physical death, and if they couldn't die, then they obviously couldn't receive a new resurrection body in place of the terrestrial one which they never lost! Christ deliberately, (and lovingly I might add,) withholds the benefits of his sacrificial death to a believer who is yet alive on earth, to justify the physical death of that believer, to the end of justifying the granting of a new resurrection body in place of the former earthly body that was forfeited for that purpose.
He is so very wise. Here we have a believer in Messiah who cannot die, (since the benefits of Messiah's death have been applied to their spirit/soul faculties,) and yet must die, (since the benefits of that same death have not yet been applied to the physical faculty of their body.) What a marvelous mind is at work here in our salvation! The only way that you can get a new body is to, (basically,) loose the one that you've got now, but by so loosing in order to gain, you acquire a new, celestial body that millions of eons of heavenly delight will not tarnish down to a single, glorified and happy atom. "To die is gain" in Christ, and indeed it is. Next to the benefit of the deathless, redeemed spiritual man or woman that we already have by believing in Christ, the next best gift to the whole and entire person is, (oddly enough,) the physical death of the same. For, if we earnestly covet to one day see Messiah enthroned upon his lustrous seat in glory, we could never do so through the vehicle of "flesh and blood", and so Christ temporarily allows for physical death to take place, as he could not have possibly given us a better gift if we would ever know the wonders of resurrection glory.