Michael Mesirow's earliest memory of Christmas Day is in a back office of La Rabida Children's Hospital in Chicago, helping his father tug off the heavy black galoshes and hang the red velour suit he had worn that morning to visit young patients.

At age 5, he recounts, he asked his father when it would be his turn to lead the family's Christmas tradition, though he didn't quite have the aging process figured out.

"When you're a little boy and I'm an old man, will I play Santa Claus?" young Michael asked his father, Paul.

Paul Mesirow didn't just assure his son; he made him promise to continue the tradition, a treasured if unusual ritual for their observant Jewish family. So when his father, debilitated by Lou Gehrig's disease, was unable to continue as Santa in 2015, his son kept his word.

"When my father told me he couldn't 'ho ho ho' anymore and he asked me to fill those shoes, it wasn't in my vocabulary to say no," said Michael Mesirow, now 33. "That was the promise I made 28 years ago. It's one I'll hold as long as I'm physically able."

On Monday, Michael Mesirow, who lives in Dyer, Ind., will arrive on the back of a firetruck at La Rabida, where dozens of patients _ from infant to age 18 _ anticipate the annual visit from Santa.

In memory of his father, who died in May 2016, he will don the handmade suit and silky white beard, deliver his own baritone greetings and, for the first time, take along his own son, 10-month-old Henry Paul, who, his father hopes, will one day take the reins.

"I've seen exactly what Santa Claus does for these children," Mesirow said. "I mean Santa Claus the spirit. I've literally seen kids who have difficulty walking run to see Santa Claus. That's an experience you can't duplicate."

For the Mesirows, who celebrate the Santa side of Christmas as well as Hannukah, Dec. 25 is a day full of shared rituals _ both sacred and secular. As Christians around the world commemorate the birth of Jesus, the Mesirows fulfill central tenets of their faith _ serving others and celebrating family.

"What I learned about Christmas is it's the time of year when everybody is kind, loving and giving. Why wouldn't you celebrate that?" said Michael's older sister Mandy Mesirow, 36, of south suburban Chicago. "In my mind, there was no reason for (Hanukkah and Christmas) to be separate."

Growing up in Homewood, Michael Mesirow and his two sisters, Mandy and Jenny, often opened presents on Christmas Eve before placing a glass of milk and plate of cookies out for Santa plus a carrot for his reindeer and then hurrying off to bed. On Christmas morning, they'd find the milk and cookies gone, the carrot nibbled and packages under the tree. Santa often left encouraging notes too.

Then the kids would get ready to watch their father entertain the children at La Rabida, the tiny, nonprofit pediatric hospital on the shores of Lake Michigan known for long-term treatment of children with chronic illnesses. The Mesirow children, after all, knew the real guy was back at the North Pole getting much-needed rest. Their father, Paul, was just pitching in.

"When he was at La Rabida, Dad wasn't Dad, he was Santa Claus and we never called him Dad in that situation," Michael Mesirow said. "There was a definite difference between the two people. My dad was a helper. That's all we could really see it as. He helped out Santa Claus."

Paul Mesirow donned the suit for the first time on Dec. 25, 1970, to cheer up his own father after a friend who served as La Rabida's Santa died. Then a 17-year-old football player at Bowen High School on Chicago's South Side, he assured his father that he wouldn't let down the kids. He kept his word for the next 44 years.

Through the years, he embodied the role.

Instead of using the hospital's Santa suit, his then mother-in-law, a seamstress, made him his own ensemble trimmed with fur and embellished with gold embroidery. Professional wig-makers crafted his silky white mane. And as he aged, he grew his own white beard and filled out the suit with his own girth. He played Santa elsewhere too. But the handmade suit was reserved for the children at La Rabida.

La Rabida's president, Brenda Wolf, is one of many Jewish employees and board members who, like the Mesirows, have made Christmas Day at La Rabida a family tradition. While no one could replicate Paul Mesirow's larger-than-life Santa, Wolf said, his son has mastered the role with his own touch of tenderness.

"Michael and Paul have presented to me what Santa and Christmas are all about," Wolf said. "It's not just walking into a room and saying 'ho ho ho.' It's the sensitivity to each child, some of whom get a little freaked out by Santa, others who are so excited and waiting until Santa gets to their room."

For some children, that means dropping down to the floor to meet patients on their level. For others, it means pressing a mask against his beard and wearing a paper gown to greet a patient in quarantine.

In recent years, La Rabida has begun to care for infants who have spent their first months in neonatal intensive care units. One of those children is Colin Fitzgerald, who was born in March 2016 with a congenital condition that caused his liver and intestines to move into the chest cavity. He was still on a ventilator and feeding tube when Santa arrived at La Rabida last Christmas.

"To have Santa come, to be able to spend Christmas with him there and celebrate it and not feel like you're in a hospital and your kid is sick, it felt like a family's Christmas party," said Colin's mother, Elizabeth. "It makes it special for the kids to keep everything normal."

Wolf said it's impossible to quantify the impact a visit from Santa can make on the children, their parents and the hospital's staff.

"They're really performing one of the most important mitzvahs they can do," Wolf said, referring to the Jewish term for good deed. "What they do is just making so many people happy."

Rabbi Leonard Zukrow, the spiritual leader of Temple Beth El in Munster, Ind., said that when he arrived five years ago, he was surprised, if not a bit bewildered, to learn that Santa was a member of the congregation. He was even more surprised to learn the level of Santa's observance when Paul Mesirow once scolded the rabbi for breaking the Yom Kippur fast 10 minutes too early.

"I had trouble squaring where he was on this continuum," the rabbi said. "It wasn't until I really understood this had been a long-standing tradition that really came out of his desire to be there for these kids to serve them. Then it all made total sense."

"We have a notion of generation to generation in Jewish life," the rabbi said. "Serving others is a key component of what we're mandated and obligated to do. Michael carrying forward that tradition, that's a wonderful tribute. Judaism requires us to reach out to the most vulnerable and children who are ill are the most vulnerable. If we can bring them a moment of joy and happiness, then we really bring heaven and earth together. Michael inhabits that part of Paul, and that part of Paul lives in Michael and certainly in Henry."

For Michael Mesirow, having Henry has added to Christmas a spark of magic that was missing last year _ the first Christmas without his father.

"For me it's exciting, but it's kind of sad," he said, bouncing his son on his lap in front of a twinkling Christmas tree. "Sad because of how my father would have looked at it, how proud he would have been. But I'm hopeful too. I know what it was for me as a kid. I know how exciting Christmas morning was. ... I hope that he will be excited to be a part of that. And then who knows? One day when he's willing and able, he'll be able to do the same and fill those shoes. I hope I live to see that too."

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