Why Obama Decided to Sing 'Amazing Grace'

President Obama's singing of "Amazing Grace" during the eulogy for Rev. Clementa Pinckney, who was killed last month in a shooting at a Charleston church, has been widely acknowledged as one of the most powerful moments of his presidency.

But when he first raised the idea with first lady Michelle Obama and senior adviser Valerie Jarrett, it was met with skepticism.

"Why on earth would that fit in?" the first lady said in reaction to the idea, according to Jarrett, who was with the Obamas as they departed the White House aboard Marine One on their way to the funeral in South Carolina.

Jarrett, who had once before tried unsuccessfully to dissuade the president from signing a line of Al Green's "Let's Stay Together," had a more subdued reaction. "Hmmm," Jarrett reacted.

The president went on to explain his thinking to Jarrett and the first lady, who had yet to read the president's prepared eulogy, during the helicopter ride.

"I think if I sing, the church will sing with me," Obama said, according to Jarrett, who recalled the story during a question answer session at the Aspen Institute's Ideas Festival.

But even then, President Obama hadn't made his mind up whether he would in fact sing.

"I don't know whether I'm going to do it, but I just wanted to warn you two that I might sing," Jarett recalled him saying. "We'll see how it feels at the time."

But as soon as the president took to podium to begin the eulogy, Jarrett said, it was clear the mood was right.

"From the first time he started to speak, the church was clearly with him," Jarrett said. "He knew they were with him."

Before the president began to sing, Jarrett observed that the president paused for a moment. And she later asked him, "Were you thinking about whether or not you were going to sing?"

"Oh no, I knew I was going to sing, I was just trying to figure out what key to sing in," the president said in response to Jarrett.