I believe there universe is so large because His original intention was for us to do exactly what he said to do, “be fruitful and multiply”, on a far grander scale than what we’re limited to on a single planet. I also believe that’s the final reward God has for those trust and obey Him; man restored to being capable of doing what God originally intended before man chose to obey himself rather than God.
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A quite similar thought has crossed my mind a few times too.
No idea how accurate it is, but whatever the good Lord has in mind I bet it’ll be far better than anything we’ve imagined.
Considering all we've seen in just the past hundred years and the interstellar travel soap operas or science fiction from novels and movies, the above is something incredible to think about.