According to Edgar Cayce, through what means do the planets effect us at the time of our birth?

I was reading about Edgar Cayce and his astrological prophesies. He said that the planets influence us because we have spent past lives on those planets. He also said that we choose what time we are born. I am wondering why the planets positions at our births would influence our whole lives, according to Cayce. How do their positions at our birth actually give us drives/inclinations according to Cayce?