The bronze blade and the fact that the miracle was always performed in Valerie's mansion seem like the clues for a magnet solution. The strength of the magnets involved seem implausibly strong unless we're playing fast and loose with physics.
Could be magnets as other said, could be some sort of electric currents (although that is practically magnets at this point)
God I love this series, I honestly don’t know
I get the whole homing knives caused by magnets thing (since I predicted it) but I still don’t get how the priest guy makes the knives float. Maybe his hands and/or clothes are coated in some substance that makes them act like magnets that push away? Kinda fits the whole “I gave you your powers” thing the head priest said.