Let’s talk about the complexity of this tweet.
He is saying that we ought to pray for our priests that they may always adhere to their vocational call. Papa Francisco is saying that our humanity is flawed and priests, being human beings, make mistakes. For the laity, it is important for us to support and pray for our priests. They are at the frontlines of the spiritual battlefield. The devil would logically attack priests with temptations and worldly inspiration because without priests we have no sacraments, no Eucharist, no Church.