(MANDEL NGAN/AFP/Getty Images)

ATLANTA - President Obama said today that he is motivated by the knowledge that "but for the grace of God … I might have been in prison," in a commencement address at historically black Morehouse College, where he spoke frankly about race and young men's responsibilities to 500 male graduates.

In his second commencement address of this graduation season, the president called on the graduates to set examples for others and reach out to those who need help, telling them that as a black man he felt a unique connection to assist those in need because he could have faced similar circumstances.

"There but for the grace of God go I, I might have been in their shoes. I might have been in prison," he said at the commencement ceremony at Morehouse College. "I might have been unemployed, I might not have been able to support a family, and that motivates me."

The president said that many young black men "make bad choices," but told the graduates, "We've got no time for excuses," because the difficulties they've faced "pale in comparison to the hardships previous generations endured, and if they overcame them, you can too."

"Growing up, I made quite a few myself. Sometimes I wrote off my own failings as just another example of the world trying to keep a black man down. I had a tendency sometimes to make excuses for me not doing the right thing. But one of the things that all of you have learned over the last four years is that there is no longer any room for excuses," he said.

The president spoke in extremely personal terms about growing up without a father present in his life, attributing his upbringing to his "heroic single mother," and said that his legacy will be defined by his success as an active father and husband, a role he encouraged the graduates to adopt in their own lives.

"My whole life, I've tried to be for Michelle and my girls what my father was not for my mother and me," he said. "I want to break that cycle where a father's not at home, where a father's not helping to raise that son or daughter. I've tried to be a better father, a better husband, a better man.

"I know that when I am on my deathbed someday, I will not be thinking about any particular legislation I passed; I will not be thinking about a policy I promoted; I will not be thinking about the speech I gave; I will not be thinking about the Nobel Prize I received," he said. "I will be thinking about that walk I took with my daughters. I'll be thinking about a lazy afternoon with my wife. I'll be thinking about sitting around the dinner table and seeing them happy and healthy and knowing that they were loved. And I'll be thinking about whether I did right by all of them."

The president, who received an honorary degree from the school, honored one of the college's famous graduates, Dr. Martin Luther King Jr., who "helped to forge the intellect, the discipline, the compassion, the soul force that would transform America."

"He, in turn, taught others to be unafraid. And over time he taught a nation to be unafraid and over the last 50 years, thanks to the moral force of Dr. King and a Moses generation that overcame their fear, and their cynicism, and their despair, barriers have come tumbling down and new doors of opportunity have swung open," he said. "Laws, hearts, and minds have been changed to the point where someone who looks just like you can somehow come to serve as president of these United States of America."

Rain poured down on the crowd throughout the ceremony, forcing many in attendance to don plastic ponchos, and thunder rang out and lightning flickered in the sky as Obama wound down his speech. The president stayed dry on stage but sympathized with the rain-soaked graduates and attendees, even noting that his wife, Michelle Obama, would not be pleased with the rainy day because of what it would do to her famous hair.

"You all are going to get wet, and I'd be out there with you if I could, but Secret Service gets nervous. So I'm going to have to stay here dry, but know that I'm there with you in spirit," he said. "Michelle would not be sitting in the rain. She has taught me about hair."