Numerous configurations for considering how and why the soul may be immortal may be developed with causality made by the Creator or without. The souls could be regarded as a naturally occurring development in a given Universe that would be replicated inevitably in the same way that the natural form of a hydrogen molecule would recur in any Universe of a similar composition to this one. Because this is a Christian philosophical contemplation though, I prefer to write of the way that God in his glory maintains the immortality of the soul.
It is always fair to say that the soul is immortal that lives in the transcending kingdom of God yet this essay is intended to approach the answer in terms that may be understood by those interested in natural philosophy as well as spirituality.
For one; a soul may be described as that content of sentience and personality, body and mind that comprises an individual. God created that content in mind before the beginning of the Universe, as he did foresee and create a particular number of individual souls to be and become in their own appropriate time. Thus it is obvious that God may restore a soul to actual being though the physical body has perished. It is possible to compare the soul to a computer operating system; if it is wiped out the computer operator may restore it from an original off-line. Obviously God has omniscience of all a priori for he has created all a priori and determined when and how any Universe or thing within it will actualize.
A soul like everything within a created and actualizing Universe has a deterministic character as well as indeterminate characteristics within it. Indeterminism embedded within determinism is an innate characteristic of a Universe with sentient beings within its nature. Variable ranges of freedom within a pre-determined, evolving temporal system exist to allow sentient will to express intelligence and intelligent design of components to exist within the deterministic physical order. In that regard human beings become ‘as little gods’.
A Universe has a given number of dimensions and time axis as boundary conditions, although it is theoretically possible for those to change within a Universe’s historical expansion though with a probability of catastrophic consequents. The boundary conditions and initial endowment of energy that may ossify or evolve into mass steady state are pre-determined to occur within forms possible with the boundary parameters of a particular Universe. Branes, strings, quarks and other energy packets that compound to comprise atoms, molecules and observable mass combine and recombine in pre-determined forms that are pre-determined and finite possibilities of that Universe.
The glory of God expresses Universes and sentient beings to exist providing the opportunity for those beings to praise the glory of God-and rightly so. The ineffable wisdom of the ancient of days transcending space-time parameters coordinates and orchestrates the harmony of dimensions and energy to evolve being perceptible-to-others created with the divine will.
One wonders if dimensions give some boundary conditional curvature to draw the energy endowed to a Universe along space-time lines of evolution, or if the second law of thermodynamics and quantum uncertainty of virtual particles are flowing along a temporal axis of charge and change re-energized to complete its course at the conclusive pre-destination at time equals omega. That re-destination would be unchanged within expansive or contractive future evolutionary cosmological courses. Human souls actualize and the for-themselves fade out within the phenomenal history of a Universe comparable in that regard to virtual particles appearing as from the slope of zero-point energy space uncertainty.
Gregory Cantor and Kurt Godel developed the ideas leading to trans-finite series, trans-finite sets and the problem of a set-of-all sets. God is the Great Spirit enabling a set of all sets to exist for-Himself actualizing His ideas with Universes being-for-others.