What constitutes a soul's individuality?

The individuality of each soul-germ is indestructible―it is a minute unit in the vast ocean of soul life, but it is still a distinct unit with its own personality or ego. 

It is this very individuality which constitutes its immortality, for it is impossible to disperse or destroy the soul. 

Imagine a body so light that the most etherealised vapour is heavy beside it, a body possessing such power of cohesion that it is utterly impossible to disintegrate its particles and the less it is bound by any element, its power of resistance against all material or spiritual forms of matter is equal to that which a bar of steel offers to a cloud of vapour. 

Imagine this and you will realise how it is that a spirit can pass with ease through solid doors and walls of earthly matter. 

It is not the soul essence, but its dense envelope which imprisons the spirit on earth or in the spheres. The walls of earthly houses offer no impediment to free ingress or egress to the spirit, and it passes through them as easily as our earthly bodies pass through fog.

This is what happens when a spirit passes through a material door or wall.