The usual idea (in modern life) is that if the self (unique person-hood - individuality) is temporal and temporary - then the self is swallowed-up when embedded in the context of eternity.
Or, the self becomes utterly insignificant when set in an infinite frame.
This is why some people find contemplating the stars to be a disturbing experience, or contemplating 'life' in general.
Maybe they are correct: if the self is temporary, then in eternity its significance is one divided by infinity.
So, for the self to be significant - the self must be eternal.
Indeed, simplistically, it makes most sense if the self is eternal in both directions: before birth as well as after death.
By this common sense kind of analysis, the choice lies between a self that always was and always will be, and the self as insignificant.
Either the significance of the self is an illusion (lasting a short time, some kind of meaningless, accidental by-product of our form of 'life'); or else the importance of the self is extraordinarily great - divine.
And ultimate and permanent reality, the eternal universe, contains many, many selves; of which we, you and I, are - and always have been and always will be - two.