Whether spiritual or physical, fatherhood is the calling of all men, Pope Francis said at his homily for daily Mass at the Saint Martha House in the Vatican.

"All of us, to exist, to become complete, in order to be mature, we need to feel the joy of fatherhood: even those of us who are celibate," taught the Bishop of Rome June 26.

"Fatherhood is giving life to others, giving life…for us, it is pastoral paternity, spiritual fatherhood, but this is still giving life, this is still becoming fathers."

The first reading at the Mass told of God's promise of children to Abraham, and Abraham's sacrifice in thanksgiving for the promise.

Abraham "felt that the Lord loved him deeply, that he had promised him many things, but felt in need of offspring. He felt within him that cry of nature: I want to have a son."

The patriarch told God of his desire "to become a father," Pope Francis said, adding that "when a man does not have this wish, something is missing in this man…something is wrong."

This "is a grace that we priests must implore: the grace of pastoral fatherhood, of spiritual fatherhood."

"Indeed, although we can all have sins, even many sins. But not having spiritual sons and daughters, not becoming pastors, is equivalent to an incomplete life, that stops half way."

"And therefore we have to be fathers, but it is a grace that the Lord gives."

The Roman Pontiff reflected on Abraham's sacrifice, in which he slaughtered and divided several animals, which birds tried to devour – but he "drove them away," according to the reading.

"I find it really moving to see this 90 year old man, stick in hand, defending the sacrifice…it makes me think of a father defending his family, his children."

This grace of spiritual paternity, and defending one's sons, is so needed for priests, Pope Francis said.

The Mass was concelebrated by Cardinal Salvatore De Giorgi, the archbishop emeritus of Palermo. He was celebrating the 60th anniversary of his priestly ordination, and some 80 priests and friends of his attended the Mass.

"I don't know what our dear Salvatore did," the Pope said, "but I am sure that he was a father."

"And this is a sign," he said, noting the many priests who had come to honor the cardinal's diamond anniversary. "It's up to you," he told them, since every tree "bears its own fruit. If it is good, the fruit must be good, right?"

"So, do not let him look bad," Pope Francis jested with Cardinal De Giorgi's priest friends.