User blog comment:B214/Question & Answers 5/@comment-172.56.5.245-20150502030816/@comment-3965848-20150502113220

So exactly anyone can pick up the hammer if they're strong enough but has to be worthy in order to use the hammer's power, or in Issei's case receive divine protection/blessing from a diety.

P.s: I checked and it's stated that the hammer was originaly meant to be as light as a feather.