While walking with his wife Chanie near Central Park last year, Peretz Chein, the 30-year-old rabbi of the Chabad House at Brandeis, watched runners of all ages complete the 2005 New York City Marathon. It was then, in a moment of inspiration, that he decided to attempt something you don't often expect from a rabbi."I thought to myself, 'I could do this,' and I told it to everyone next to me," Chein said. "They laughed at me."

Nobody was laughing Sunday when Chein successfully completed the 29th annual Cape Cod Marathon in Falmouth, Mass., finishing the 26.2-mile course in four hours and 17 minutes to come in 556th out of 970 runners who made it to the end. He had never run in a marathon before and hadn't engaged in any sports since the age of 13.

Chein's motivation for this endeavor was more spiritual than athletic. At Chabad's Shabbat dinner one week after his trip to New York in 2005, Chein spoke to Brandeis students about the importance of doing things in life that are so beyond them that they never even considered trying, with the goal of inspiring students to do good deeds in Judaism they never thought were possible. Teaching by example, Chein promised the crowd that he would run the full 26.2 miles of a marathon within the next year.

"What I try to do with my life is to inspire people to do new things, particularly within Judaism," Chein said. "I wanted to prove to myself that what I try to inspire within others is possible, while motivating them to do the same."

He also said he believes in the power of sports as a motivational tool.

"Sports requires more than physical ability," Chein said. "To me, it is predominantly about motivation, focus and spiritual ability. Therefore, sports can be a tremendous vehicle to inspire."

But even after Chein's bold guarantee, he felt underestimated.

"At the time, it just seemed like nice speech to the students," Chein said.

"When Peretz told me he was running, I suggested that he do a half-marathon," said Victoria Ornstein '06, a Brandeis Chabad board member.

But on Sunday, Chein exceeded all expectations, including his own, by finishing the marathon as quickly as he did. His wife and several students who attended even missed him at more than half of the scheduled checkpoints during the race. "He was running so fast and ahead of schedule," Ornstein said. "We couldn't keep up with him."

"I didn't expect to run at such a quick pace," Chein said.

Chein faced extremely windy conditions during the race, as well as a long stretch of rolling hills on the second half of the course, which he was informed of just days before the event. Although he started feeling wear and tear toward the latter portion of the marathon, Chein still managed to finish in impressive time.

"I was confident that I would finish throughout the race, and my adrenaline was really pumping," Chein said. "The first 15 miles were a breeze, but it got really tough around the 18th mile."

In order to train for the marathon, Chein ran predominantly in Waltham and on the treadmill. He said it wasn't easy for him at first.

"After I made my promise, I got on the treadmill for 10 minutes until my lungs and legs told me, 'Peretz, get off,'" he said. "I was wondering what I had gotten myself into."

But despite his initial struggles, Chein knew he could not go back on his word.

"I realized that I had a responsibility to deliver on my promise," he said.

A week and a half before Sunday, Chein ran for 21 miles, assuring himself he was capable of completing the race.

If Chein's idea was to provide inspiration through this feat, he certainly accomplished his objective. "I always looked up to him, and this really taught me about focus and determination," Chanie said.

"To see a grown man with two children and a wife run a full marathon and do so well is incredibly inspiring," Ornstein said. "We were all blown away by his perseverance.