"I will give to priests the power to touch the most hardened hearts."
The only power a priest has is to bring Jesus to others. Of course, in a unique and special way; as someone delegated the authority from Jesus Himself to act in His Name - sanctifying, teaching, absolving. But this power goes nowhere unless the heart of the other opens itself to the power of the priest to sanctify, teach or absolve him or her. Until then, a priest is powerless in the face of indifference or even hostility.
What can open a closed heart? Only an open one. As wide open as the Heart torn open by the stab of a spear as He hung upon the cross. No matter how closed a human heart is, it naturally responds to love. The more closed the heart, the more that love must prove itself.
The priest, being human, is always tempted to give up on stubborn hearts and move on to the next. He cannot do so, if he is to follow the Good Shepherd who leaves the safe sheep in search of the lost. The priest must lay down his life, not just for the safe and sound sheep, but for the lost one. Where will the priest find this supernatural love and will power to do this? He will find it, if the priest is devoted to the Sacred Heart. If the priest opens his heart to the One Heart that alone can truly save.
Then it will be the Sacred Heart who works through the priest, and not just the priest preaching, teaching and working with his natural abilities alone. How often has Jesus used the less talented priest to win so many souls! Less talented perhaps, but a priest more fully devoted to Jesus and therefore a better instrument of the Lord. Truly, nothing depends more for the success of a priest than his total surrender to Jesus, who will work through the such a priest despite his limitations.