It would feel wrong to us if our God made it a condition of our
eternal life that we should befriend Him in a personal way, so we enhance the
meaning and value of that friendship when we realise that it is an unconditional
choice, just as real friendship should be. But there is also nothing wrong in
choosing to unite with all the beautiful values and qualities which belong to
the Divine Impersonal Being. Therefore if we unite our impersonal nature with
the impersonal nature of God, then that is a proper expression of our Divine
William Arkle - Caption to a painting
My understanding of this, would be that a person who chose to unite his impersonal nature to the impersonal nature of God would be someone who either simply did not, or could not, believe in God as a person; or who did believe in a personal God but could not love him - or, it may be a person who rejects the gift of consciousness which comes from being a Son of God (one of the Children of God).
My understanding is that humans have an unique personal spark, some essence which precedes us becoming a Son of God - and it is this which is the cause of our autonomy, our free will.
When we became Children of God, to this personal spark was added a spark of God Himself - and this spark of God is what made us conscious, aware, capable of relationships (and that we all share this spark is what makes us really and truly children of God, brothers and sisters in Christ).
But the spark of divine consciousness brings with it attachment, especially empathic pain, worry, regrets, sorrow - all the intrinsic realities of family relationship - and some people find this awareness simply too painful, a source of intolerable suffering.
At a profound level such persons reject the spark of God, and yearn to return to their original state of being an unique personal spark yet unaware, unconscious, assimilated to the universe.
To such souls, God provides the third option - neither Heaven nor Hell but the opportunity to "unite with all the beautiful values and qualities which belong to
the Divine Impersonal Being" - in an unchanging, eternal, present state without memories or anticipations.