The ancient god was born mystical. When the 'world' was first formed, it was empty and lonely, so perhaps this was why god was born inexplicably due to some mysterious reasons.
He was born with unlimited power, since he was an inherent extraordinary existence, entirely unlike those who acquired and raised their ability to the limit of the mortals and then transformed by chance. He was also unlike those common gods who inherited extraordinary power by chance before relying on setting up a new religion to confuse the sentient beings to absorb their power of faith so they could maintain and enhance their strengths. It seemed as though the mortals' ignorance had forcefully group these two together, but in actual fact, they were firmly related to each other.
In ancient times, those who had the opportunity to gain the power of faith were all descendants of the old god.