Now she fully understood why Celestia was so determined to help the poor humans, and why Equestria had bothered to invade the earth.

Humans were intelligent, fully self-aware, fully conscious, fully sapient beings. But they had been so unfortunate as to arise in a universe without any magic to speak of. Souls were only and purely magic. If anything at all in all of existence was a magical thing, a spirit, a soul, absolutely, completely was. These poor, naked apes were self aware, they understood their mortality, but they were little more than chemical machines. For this species, in this universe, dead... was dead. When the machine stopped, they stopped, and that was the end of them. Each precious one of them was an entire cosmos of dreams and thoughts and hopes and fears just by themselves, yet all were nothing more than chemicals and electricity banging around a primate skull.

Conversion turned that chemical robot into an Equestrian - that was the real reason behind powering the nanomachines of the ponification serum with the miracle of Equestrian magic. It wasn't merely to avoid conservation of mass issues, or to sidestep entropy, or to avoid generating heat. No. Ponification serum was what it was so as to infuse and transform those chemical, molecular-machine human minds with a truly living lacework of real magic, so that they, as ponies, could join the eternal herd. The true purpose of Conversion was to grace the poor ape robots with nothing less than souls.