How do Christians who believe that eternal life begins now explain the fact that Christians die?

The question

If eternal life is something that Christians experience now, then how is this reconciled with the fact that Christians die for multiples reasons (e.g. car accidents, diseases, natural disasters, etc.)? If Christians have eternal life now, why do Christians die?

Short Answer

In this current age Christians do not have to deny the stark realities of physical death and taxes. Even the 12 apostles died (11 as martyrs) and so did countless canonized saints. Jesus paid taxes too, and died in his human nature. So how to understand verses you quoted (John 5:24 and John 3:36) without contradicting ourselves? When spiritual realities break our understanding what we can do is to redefine our terms.

First, a word about terminologies:

• If we study the Bible in depth and if we let the Bible itself define the meaning of the terms it uses, the key concept "life" in the Bible cannot be reduced to "biological life" as discoverable from the study of Biology. So methodologically it is incorrect to understand "eternal life" by simply pairing the word "life" understood from biology with the adjective "eternal" and expect that God will work out "eternal life" according to our conception!
• We shouldn't confuse "eternal life" with "immortal soul". The Bible is clear that ultimately life is given by God, which God then "implements" according to His design for humanity. He alone creates our souls and "engineers" of our bodies, whether the current mortal version or the glorious version.

For believers, eternal life has to be understood as being with Christ eternally:

• who indwells within us and whose ministry removes from us the fear of both physical and spiritual death (God sustains both our body and soul, Matt 10:28)
• who is present at the moment of our death
• who is present with us in the intermediate state
• who will be with us in the new heaven and new earth

thus showing how our soul (who is a hybrid that possesses the unique ability of being able to comprehend eternity and time) can benefit from Christ's eternal presence with us starting now and uninterruptedly through the stages above. This is the meaning of "eternal life" I propose in this answer.

Why doesn't God give us eternal body now to believers who have the indwelling Holy Spirit? We can only say it's part of God's redemption plan, from hints in the Bible (see the sections below). At least he is being fair: all people (including Jesus) pass the threshold of dying physically. Healing and miraculous resuscitations were meant to be temporary as an aid to faith. Only Jesus had resurrection to the new body.

The best explanation that makes sense to me is (note: this is pious speculation, not doctrine). Our bodies "made from dust" are not the body God ultimately intended human beings to have in the first place. We were meant to have bodies "from heaven". The plan was interrupted by the Fall of Adam, which Christ reversed with the redemption plan but which He has not yet finished. Hence we still need to relinquish this body "from dust" to go back "to dust". Cue the words of the priest whom our survivors will hear at our funeral from the Book of Common Prayer:

we therefore commit this body to the ground, earth to earth, ashes to ashes, dust to dust; in sure and certain hope of the Resurrection to eternal life

BUT we can start living eternal life with the sure hope of anticipating being given bodies "from heaven".

Note about Christians holding the mortalists and Annihilationists view

Christian mortalists, who some also hold the view of Annihilationism need only do slight adjustment to my answer:

• In the Bible "eternal life" is the language primarily used for believers / the righteous as opposed to the wicked whose souls will be annihilated. So my answer doesn't apply to the annihilated wicked at all.
• Christian mortalists who are saved believe their souls are either sleeping or destroyed after physical death. But if they follow "eternal life" as defined in my answer their certain hope of resurrection can enable them to live in this mortal soul in union with Christ already, the memory of which God will transfer to the new body and soul. In other words, the effect of union with Christ is the same with those who believe in the conscious intermediate state.

Additional perspectives

1. We live in the in-between overlap of the current age and the age to come

According to the Biblical paradigm of already but not yet (see also this article from desiringGod) we already have eternal life but the full extent of redemption is still being worked out as Christ himself is still fighting with the church militant (1 Cor 15:25-26):

²⁵ For he must reign until he has put all his enemies under his feet. ²⁶ The last enemy to be destroyed is death.

(Source David Briones's article)

(Source: Kim Riddlebarger's blog post, pdf version here)

As adopted brothers and sisters of Christ (who already receive eternal life), we need to join with Him to participate in the inbreaking of the Kingdom of God on earth by fighting injustice, expanding the reach of the gospel, and rescuing the oppressed. All these fighting can result in suffering and premature death but when joined with Christ nothing can separate us from his love (Rom 8:31-39). In this sense, whatever "old body state" we are in, our soul already starts living eternally without contradicting ourselves even when we die naturally or prematurely (God forbid) because of cancer, covid, crime, etc.

In the mean time (the not yet portion), we are still awaiting to be given the glorious bodies which cannot die and creation as a whole is still groaning for redemption (Rom 8:22) until there is the new heaven and earth.

2. More on the eternal life on earth as life in union with Christ

The two resources you linked already contain enough information about what Christian concept of eternal life is, which is essentially the life with the eternal Christ which started when we received the gift of spiritual life in the here and now at the point of baptism / conversion (depending on your denomination). This eternal life is a life of personal relationship with God where we voluntarily align our will to love with God's will to love despite:

• the risk of dying a fighting soldier/martyr for God's cause in the world
• the natural effect of decaying body (diseases, involuntary car accident) and natural disasters
• the natural result of evil in the world (victim of DUI car accident, wars, etc.)
• incurring the wrath of the world while we shun the life of sin to avoid contaminating this spiritual life as we are continually being transformed from our tendency to sin (even St. Paul was still struggling, Rom 7:14-25)

Job from the OT provided a great example of trusting God despite suffering the mortality of his body, and so did Paul from the NT. Both trusted the eternity of God and conceived eternal life as primarily "staying close" to God. Thus Job refused to curse God and die as his wife suggested him to do, because to her God didn't live up to the bargain of rewarding the righteous with health and prosperity, and not worth worshiping. Instead Job expressed his trust as follows (Job 19:25-27):

“But as for me, I know that my Redeemer lives, and he will stand upon the earth at last. And after my body has decayed, yet in my body I will see God! I will see him for myself. Yes, I will see him with my own eyes. I am overwhelmed at the thought!

It is our responsibility to nurture this life by continuing to be united with Christ as he vine (John 15:5) and by walking in the spirit (Gal 5:16-17). From our point of view, this life is one of active receiving of grace from the 3 Persons of the Trinity, who indwell in our soul as eternal life. which is why at the end of most church services there is this benediction being said (from 2 Cor 13:14) while the congregation's hands are usually in the receiving mode (palms up):

The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.

Some denominations teach that this eternal spiritual life can be lost, but this should not factor into our discussion here. What is clear is that as long as we keep being united with Christ, nothing (including death) can separate us from the love and continual forgiveness (as we keep repenting after we sin) that comes from the indwelling Trinitarian God (Rom 8:31-39).

3. It is God's plan that the Tree of life is not yet available for believers

There is a good case to be made that even Adam, being made of dust, did not yet have eternal life before he ate the fruit from the Tree of the Knowledge. After the fall, the Tree of Life was barred from him, and from us as well. From this perspective, for those united with Him, Christ reversed the curse of the Fall (which at least includes 'spiritual death' as separation from God) but He has not yet given us the fruit from the Tree of Life (eternal bodily life). Hence, like Adam before the Fall, we still have our mortal bodies created from dust. We are also still suffering from the other effect of the fall (for which the whole creation is still groaning) which includes hard labor toiling the soil for men and painful pregnancy for women. But like Adam before the Fall, we have at least received the "down payment" of guaranteed eternal spiritual life while awaiting the glorious body given "from heaven" instead of "from dust" (1 Cor 15:45-49):

⁴⁵ Thus it is written, “The first man Adam became a living being”; the last Adam became a life-giving spirit. ⁴⁶ But it is not the spiritual that is first but the natural, and then the spiritual. ⁴⁷ The first man was from the earth, a man of dust; the second man is from heaven. ⁴⁸ As was the man of dust, so also are those who are of the dust, and as is the man of heaven, so also are those who are of heaven. ⁴⁹ Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven.

For more information, please read a 2018 article by Joshua Van Ee from the Carl F.H. Henry Center for Theological Understanding website: Was Adam Created Mortal or Immortal? Getting Beyond the Labels.