Picture again the Christmas morning newspaper photograph of altar boys at the Vatican. Eight or so tender young boys wearing long magenta cassocks stand in awe in front of the Swiss Guards at St. Peter's Basilica. One has his cell phone and is taking a photo of a Guard. (Or is it a "selfie"?) The Guards are tall, handsome, usually from related families and dressed in their colorful yellow, blue, red, and orange uniforms. They carry swords, every boy's dream item. (They have modern weapons, too.)

No doubt these boys are carefully selected to be the elite who yake part in the Christmas Masses in Rome. We wonder how many of these young boys will want to become priests. Think of what small events had a great impact on our life choices. And one thing leads to another. One of us chose a college to attend because of an older boy from our town who could dribble behind his back. Long ago that was, indeed, a spectacular feat. One young man we know wants to be a hermit, like Jesus. He hopes to live in a cave, alone. It could be he is bullied at home and sees the cave as refuge. Or he could have a vocation.

What are the ways future priests know they have what it takes? Do many plan from early days to take the collar? Cardinal O'Malley has sometimes referred to his recognition that he wanted to become a priest when he noticed a happy monk, tending his garden. He was with his father and brothers, but his eyes saw something different from the others.

What is the spark that kindles the heart, the calling which comes to some ears and not to others? In paintings these beckonings can be dramatic as in Caravaggio's "The Calling of St. Matthew." The scene is the tax collector sitting in tavern when Christ enters with Peter and points at Matthew, an older man, to follow him. Matthew is surprised and exhibits a "Who me?" expression while pointing to himself. Here the light emanating from Christ bathes the face of a young man on its way to the older Matthew. We can suppose that other disciples will have to be young.

At one time every family expected to give a son to the Church. The others would carry on the family duties and one would be educated to become a priest. It may have been his only way to obtain an education. He would receive encouragement and trials from his teachers. He would be tested. Many are called, but few are chosen. One young priest we know has said he became a priest, in part, because people asked if he had thought about it. Their interest ignited something in his mind and spirit.

Looking around, we can find the young men. Maybe they are already altar boys, who have the potential. Surely being an altar boy is formative. We praise those who encourage their sons to take this role and training.

Teachers often see the signs for a possible vocation when their students are quite young. Someone we know well was in a class with Sister Somebody when she was giving her regular "You could become a priest lecture." It was an all-boys school. She said "Anyone in this class can become a priest -- except you and you," naming the someone we know who was particularly rebellious. Naturally he sent Sister an invitation to his ordination when he became a priest. We assume she attended.

It takes courage to even consider becoming a priest. Am I worthy? Can I endure the life? Will this decision be acceptable to my family, even girlfriends? Generally his parents will be accepting and quietly joyous as this development. They will be able to see the qualities in him needed to be a priest. He and his family know the pitfalls, the siren songs of modernity. He has to know there will be dark nights of the soul. There will be temptations. He will have to give up fathering children and, in turn, take his flock as his children. Not having his own offspring, he will be free to be part of many families.

In this world of many choices, the young man will put away boyish rebellion and cultivate the manner of a priest. He will calm his restless soul and follow the discipline. His vows will be taken seriously. The value of discipline will probably become even more evident as time passes and the fire of faith is tested.

The priest is freed from some of the modern world's preoccupations. While he hopes to keep a fit body and mind along with his soul, he will not stress over "getting ahead," or losing hair. He may be competitive, but he will not compete in the same ways as his brothers. His measure will not be taken in the usual way of the world. He will not worry if the stock market advances or retreats. He will likely give up on things beyond his control and rely on prayer.

In recent years, it has been especially difficult to be a priest, particularly here in Boston. Priests have been insulted on the street and castigated in the press, blamed for the 20 and 30 year old sins of brother priests who are long gone. In the face of questioning stares and false accusations, their faithfulness to our Church and to their vocations has been a true trial.

As people whose lives have been nourished by the priests we have known, we worry. While a few seminaries are overflowing, many are not. There aren't enough priests for all the families who desperately need their help.

While stopping by St. Mary's Church on a Saturday, we watched a father taking his young son inside. Perhaps he was coming to be trained as an altar boy. In any case, the boy's face was filled with joy and anticipation.

Kevin and Marilyn Ryan, editors of "Why I'm Still a Catholic," worship at St. Lawrence Church in Brookline.