Discerning

I'm reading a post by Joseph Moore on Yard Sale of the Mind and I come across this phrase: 

"discerned out of the priesthood"

which throws me. I've heard all of those words before, but not in that combination. What in tarnation is he talking about? A story on Catholic News Agency explains it. It concerns people discerning their calling. If they decide they want to be a priest and join a seminary, they are 'discerned in'. If they later decide that the priesthood is not for them and leave the seminary, they are 'discerned out'.