In his Message for the 51st World Day of Prayer for Vocations, Pope Francis explains the rationale of Good Shepherd Sunday.
The Gospel tells us that “Jesus went about all the cities and villages… When he saw the crowds, he was moved with pity, because they were harassed and helpless, like sheep without a shepherd. So he said to his disciples, ‘The harvest is plentiful, but the labourers are few; pray therefore the Lord of the harvest to send out labourers into his harvest.’”
These words surprise us, because every farmer knows that it is necessary first to plow and sow and cultivate. There is a lot of work before an abundant harvest. But Jesus says instead, “the harvest is plentiful.” So who did the work to bring about these results? There is only one answer: God.
Therefore, when we pray for priests and priestly vocations, we’re really praying for God’s kingdom: “Thy kingdom come, thy will be done on earth, as it is in heaven.”
Moreover, I think our Lord wants us to pray for holy priests. A priest who isn’t striving to be holy does great damage to the Church. That’s not just true of priests who do evil. It’s also true of priests who settle for mediocrity. To pray the Lord’s Prayer is to pray for holy priests.