It is a poignant moment for the son, culminating years as his father's sidekick.
"My first steps as a deacon," Chrysostomos says, "were with him."
And the experience will be replayed again in a few years, when father and son will lead another Gilbert offspring, Aaron, around the altar to take his own vows.
On this Father's Day, the question is: Was it nature or nurture that propelled two sons to dedicate their lives to the church as their priestly parent had?
Being a priest wasn't "something they saw and they liked," says Denise Gilbert, Matthew's wife."The two sons were literally born with an inherent desire to be priests."
So genes may have had something to do with it.
Matthew's mark • Father Matthew's Protestant mother died when he was 9, and his father remarried a Greek Orthodox woman. His stepmother nurtured him in the new faith, as did a Sunday School teacher and parish priest in Bethlehem, Pa.
For him, there was no aha moment of decision, only an ineffable tug toward the priesthood.
"It's a calling," he says. "You just know."
Denise, whose parents were Greek Orthodox, also felt drawn to the priesthood from an early age.
"When I was a little girl, I would watch the priest serving the divine liturgy on Sunday mornings," she says, "and I wanted a life like that."
God heard "the desire of my heart," she says, and drew her to Boston, where she met Matthew, who had "a humility in him that I haven't seen in very many others."
Together, the couple reared six children five boys and one daughter in the church, where they were embraced in that Christian community and taught the gospel of Jesus Christ.
The church has given them purpose and identity. Now, Denise says, it's their turn.
"God has been so merciful to us," she says. "The least we can do is to give our children back to him."
All six kids have chosen service-oriented careers a nurse, a social worker, a public service lawyer, and the two priests. Another one is contemplating becoming an Orthodox monk, which would require him to live in a monastery.
Each path is different, of course, even for the priest brothers one has chosen lifelong celibacy and the other is engaged to be married.
Parallel spheres • The Greek Orthodox Church views marriage and celibacy as equally valid ways to serve God.
"Orthodox churches show no preference for one at the expense of the other," according to the Orthodox Research Institute, an online reference library, "preferring not to advance theological reasons in justification of one option rather than another."
Quoting Clement of Alexandria, the institute says, "celibacy and marriage each have their own functions and specific services to the Lord." Because of this, "we pay homage to those whom the Lord has favored with the gift of celibacy and admire monogamy and its dignity."
The church believes the choice dates to Christianity's earliest days, when some of Jesus' disciples were married and others were not.
Centuries later, the Eastern churches split from the Roman Catholic Church over a variety of issues, including the latter's mandatory celibacy for priests. In the East, there continued to be choices, though bishops had to forgo marriage.
Today, the rules are clear: A priest can be married, but he must wed before he is ordained. If he divorces, he can remain a priest only if he remains celibate. If he remarries, he loses his priesthood. Bishops, on the other hand, are still drawn from celibate priests (although most parish priests, like Father Matthew, are married). Monks are also celibate and live together in communities.
The eldest child in Gilbert family, Deacon Chrysostomos treasures his parents and siblings. He plans to continue to draw on those relationships. But the decision to be celibate, he says, was not difficult.
"Everything in my life is the church," he says, from his office at the church's North American headquarters in New York. "I have felt called to this since I was a little boy. I want to give my life to it for the rest of my days."
When he was 11, young Christopher chanted during services, when his father had no one else to do so. The son went on visits, met the sick, observed every element of the divine liturgy, practiced intoning the holy Greek verses.
It was awe-inspiring, he says, to watch his gentle, keenly discerning dad act as "spiritual father" to the whole community, ministering to those in need during their most joyous times as well as through their deepest sorrows.
Now, the extroverted 28-year-old says, his father sometimes calls him for advice.
"Our roles have somewhat shifted," he says, adding, "and matured."
Soon it will be Aaron's turn.
Mirroring dad • Not long after Aaron the fifth child was born, the family members settled first in Price and then, in 1999, Salt Lake City. Before that, they had lived in Chicago, Spokane, Wash., and several places in California.
The children were used to making new friends and to being considered outsiders, while bonding to one another through evening prayers and daily scripture reading.
Despite his ever-growing religious responsibilities, Father Matthew always managed to find time for basketball, hiking, camping, long trips in their 15-passenger van and impetuous ice cream outings.
Through it all, young Aaron sensed his own growing vocation for the priesthood, he says. "I always felt Christ calling me."
So the quiet, studious young man ("a real thinker," says Chrysostomos) graduated a year early from Riverton High, so he could get started on his journey.
Aaron left at 17 for Hellenic College Holy Cross School of Theology in Brookline, Mass., described as "the intellectual, educational and spiritual center of the Greek Orthodox Church in America," where both his father and brother had studied.
He graduated this year and is home for the summer, where he like his older brother once did will accompany his father-priest through all his assignments, taking part in services and helping church members.
Aaron is similarly moved by watching his dad "doing God's work with sincerity and earnestness."
The Gilberts have a saying in their family: "Have love and travel the world while serving the church," and that is exactly what the 21-year-old hopes to do.
He plans to marry in 2014 and be ordained a deacon soon after that.
The fourth child, Andrew, may one day join his brothers in the priesthood, but as a monk.
Father Matthew and Denise Gilbert, who works full time in Holy Trinity's office, did not plan to have clergy among their children, they say. It was not something they pushed or even encouraged.
But they do have another saying: What the child learns, the adult does not abandon.
That seems to have happened.
Fathers by the numbers
70.1 million • Estimated number of fathers across the nation in 2008, the most recent year for which figures are available.
24.4 million • Number of fathers who were part of married-couple families with children younger than 18 in 2012.
1.96 million • Number of single fathers in 2012; 16 percent of single parents were men.
189,000 • Estimated number of stay-at-home dads in 2012.
21,418 • Number of sporting-goods stores in 2010.
15,542 • Number of hardware stores in 2010.
7,368 • Number of men's clothing stores in 2010.
Source: Census Bureau