Mitt Romney appeared before a packed crowd of conservatives today for a mea culpa that reflected on his campaign journey across America and pleaded with activists to not let the country slip from its position as the most powerful in the world.

After his November election defeat, Romney disappeared from the public scene only to re-emerge earlier this month to relay his disappointment in a sit-down interview with Fox News Sunday.

“It kills me not to be there, not to be in the White House doing what needs to be done,” Romney said in that interview.

Today, as late for the speech as President Obama usually is for a press conference, Romney took the stage to the most massive ovation of the Conservative Political Action Conference yet.

“You have touched my heart again,” the former Massachusetts governor said. “What a sight you are. What a privilege to be here again.”

Last year, Romney was trying to convince CPAC of his right credentials, calling himself “severely conservative.”

“You were there from the very start and made a difference in my campaign,” he said today. “You gave my campaign an early boost. You worked on the front lines—promoting my campaign, turning out voters. Thank you.”

Romney said he was honored to be the Republican Party’s 2012 nominee. “Of course, I left the race disappointed that we didn’t win,” he added. “But I also left honored and humbled to have represented values we believe in and to speak for so many good and decent people. We’ve lost races before, and in the past, those setbacks prepared us for larger victories. It is up to us to make sure that we learn from my mistakes, and from our mistakes, so that we can win.”

If there was a “severely conservative” moment of this CPAC, it was Romney using that definitive tone to declare that, despite his loss, “I utterly reject pessimism.”

“We have not lost the country we love and we have not lost our way,” he said, expressing confidence that lessons learned from November will help the GOP win back the White House and Senate. “My optimism for America wasn’t diminished by my campaign — in fact, it grew.”

Not breaking stride to divert from script during occasional shouts from the audience, Romney reflected at length on people he met — from Billy Graham to Cardinal Timothy Dolan to members of the armed forces — and places he saw during the campaign.

“We are a patriotic people. The heart of America is good. Our land is blessed by the hand of God; may we as a people always be worthy of His grace, and His protection,” he said.

“Like you, I believe a conservative vision can attract a majority of Americans and form a governing coalition of renewal and reform,” Romney continued. ”As someone who just lost the last election, I’m probably not the best person to chart the course for the next election. That said, I do have advice. Perhaps because I am a former governor, I would urge you to learn the lessons that come from some of our greatest success stories: the 30 Republican governors.”

He gave shout-outs to Gov. Nathan Deal of Georgia for expanding charter schools and Gov. Rick Snyder for signing right-to-work legislation in Michigan, and “the governors of the blue and purple states, like Bob McDonnell, Scott Walker, John Kasich, Susanna Martinez, Chris Christie, and Brian Sandoval.”

The mention was notable as the New Jersey Republican wasn’t invited to the conservative confab this year.

Romney also lauded “the clear and convincing voice of my friend, Paul Ryan.”

“If I were to offer advice to any president of the United States, it would be this: do whatever you can do to keep America the most prosperous and free and powerful nation on earth,” he said, warning of the entities jockeying for world leadership: “China, Russia, and the jihadists.”

He lauded America’s role in world, including never using “hegemonic military power” to prey upon the weak, extending philanthropy to victims of natural disasters and AIDS victims in Africa, and intervening in conflicts with the goal of liberation.

“Freedom flows in American veins. It invigorates our many enterprises, it inspires us to live beyond ourselves, it calls us to care for the suffering and downtrodden. It has made us a great nation. Today, history and duty summon us again,” Romney said. “Each of us in our own way will have to step up and meet our responsibility. I am sorry that I will not be your president – but I will be your co-worker and I will stand shoulder to shoulder with you.”

Romney’s former running mate, Ryan (R-Wis.), spoke earlier in the day and similarly received a warm welcome from the crowd.

But Ryan conveyed the impression that he’s left the veep nod behind him and is once again immersed in his role as House Budget Committee chairman. He made zero mention of the campaign and gave no indication of future political goals.

“Hey, I’m so happy to be here. You know, we all need a break from the mess in Washington,” Ryan said. “And I’ve just got to say, it is nice to be in a room full of conservatives for a change.”

(Don’t miss Next Generation’s members-only coverage of CPAC 2013 — featuring former Congressman Allen West and Michelle Fields. Click here to learn more.)