One of the problems throughout the history of Christianity has been that it has sometimes been framed as this-worldly, and sometimes as next-worldly - maybe sometimes some half-way-house compromise; whereas it is actually neither.
This third-thing is not - of itself - difficult to understand; except that people will not give-up pre-existing categories of either/or, of what they already think Christianity is.
The two ways of doing this, came under categories of complete acceptance of, and immersion in, this world - or the complete rejection of this-world as merely illusion, merely-sin.
Obviously, the mainstream modern materialist way is complete and exclusive acceptance of this world, the attempt to maximize pleasure and eliminate suffering, and total rejection of everything 'spiritual'.
But there is also an allowed (and to some extent encouraged) backup - which is the permissible 'oneness' spirituality; that has been Western manufactured from elements of Hinduism and Buddhism. This aims an annihilation of all separateness, all ego and thinking, re-absorption into the abstract and im-personal divine - as much as possible during this life (by meditation), and wholly after death.
Christianity - by contrast - is about following Jesus Christ through-death, to resurrection and Heaven. Resurrection, Heaven and Jesus are all regarded as involving actual individual (free, agent) persons; and the ideal destination and state is loving and personal relationships, on earth and in Heaven.
With Christianity - those who choose salvation will remain them-selves, eternally.
Why is this so difficult to grasp? Why do so many people try to stuff Christianity into just-this-world or abstract-other-world boxes?
Simply, but profoundly, because the metaphysical assumptions of modern man regard the personal as only this-worldly; hence time-bound, changeable - always being-corrupted toward a death which is annihilation of the self.
The options for someone with such fundamental assumptions about reality are therefore either consciously choosing to accept the actuality of change and corruption - that is sin: which means denying any fundamental difference between sin and virtue; or else to yearn for a permanent escape from change and corruption that can only be into the un-conscious, impersonal, the abstract, the time-less - entailing the loss of that which makes us persons.
This explains why modern materialism can comfortably coexist with oneness spirituality - the one accepts, the other desires, annihilation of 'the self'.
And why, in practice, the advocates of other-worldly oneness spirituality are typically eagerly on-board-with the primary strategies of this-worldly totalitarianism.