Modern people assume that death is the end of everything personal, the destruction of the self; they assume that when the body dies then nothing is left.
The ancients, before Jesus, also believed that death was the end of everything personal, and that there was destruction of the self - but the difference was that after the body has died, they believed that something was left: that the soul remained.
The soul minus the body wasn't any use, it lacked self-consciousness, it could not help-itself... but the soul remained alive, like a witless 'ghost'. (The Underworld/ Hades/ Sheol was populated by such ghosts; left-over after death of the body.)
Before Jesus only a perfectly divine-aligned Man could become fully-divine; because being divine means to join with God in the creative work of the universe. To join in the work of creation, one must wholly embrace that work and its aims; to have something distinctive to contribute to creation, one must have free will, must have agency.
Therefore one must have 'a body' because the body is what enables us to have divine free will: it is incarnation that separates our will from that of God.
So resurrection - with an immortal, indestructible body - is necessary for us to become divine agents.
In sum, before Jesus divinity was not possible to a Man unless one was already fully divine-aligned. However, Jesus was a perfectly divine-aligned man, and therefore Jesus could and did become fully divine (at his baptism by John).
And that event changed everything.
After Jesus, who began as a Man, had become fully divine; then it was possible for any other Man to become fully divine, simply by following the path that Jesus had made. In other words, one needed to love Jesus, to have faith in who Jesus was and what he could do; and then anyone could follow Jesus to full divinity - but only after death, only via death.
Why only after death? Because we are not perfectly-aligned to God during our mortal lives (that is, because we are all sinners) our body must first die, before our soul can be resurrected. Our personal self must be ended before it can be remade (from the remnant soul)
This process began before Jesus himself died, with the resurrection of Lazarus. What we know of Lazarus is the mutual love between him and Jesus. Lazarus was the first Man to die who had faith in Jesus, and Lazarus was therefore the first Man to be resurrected by Jesus - but uniquely Lazarus was resurrected back into earthly life, as a miraculous sign of the new dispensation.
Lazarus then went on to write the Fourth Gospel as the 'beloved disciple', being the best possible witness to the reality of this new dispensation; and the Man who best knew the nature of Jesus and what gift he brought.
So, now, after Jesus - the Good News is that we can each and all have life everlasting and the resurrection that entails; no matter what our state of sin or how far from being God-aligned we may be. We may have resurrected life everlasting after we have died; 'simply' by loving and trusting Jesus to lead us, and by following the same path to full divinity that Jesus first took, and which (by taking) he made for us.