BOSTON — The Boston Marathon will never be just another race again. The twin bombs at the finish line of the 2013 race made sure of that.

But when the field of 30,000 leaves Hopkinton on today, the world’s oldest annual marathon will take the initial, tentative steps back toward its roots as a world-class sporting event first and a cause second.

“For us, the core principle is the Boston Marathon is an international athletic event focused on competition and excellence,” Tom Grilk, the executive director of the Boston Athletic Association, said.

“We start there, every time. Including last year,” he said. “What happened in 2013 was the closest and perhaps most poignant part of our history, but part of the history.”