On his last full day as president, Barack Obama on Thursday released a love letter to his country in which he fondly tells Americans: "You made me a better President, and you made me a better man."

Obama leaves office Friday after eight years in the White House, handing over the most powerful job in the world to New York business mogul Donald Trump. In his last days, Obama has hosted a farewell rally in Chicago and held his final press conference in the West Wing, where he said, "At my core, I think we're going to be OK."

Obama wrote in an open letter published on Medium that it's been a long-standing tradition for the president to write a parting private missive to be left for his successor.

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"But before I leave my note for our 45th president, I wanted to say one final thank you for the honor of serving as your 44th," Obama wrote. "Because all that I've learned in my time in office, I’ve learned from you."

The president touched on some of the more amazing events he's witnessed as leader of the free world, including finding "grace" in a Charleston, South Carolina, church after a mass shooting and seeing families blossom because of the legalization of gay marriage.

The letter came out on the same day that Obama wrote to the speaker of the House and the next Senate president about Guantanamo, in which he says 41 detainees remain imprisoned there despite his hopes of closing it before the end of his administration.

"Guantanamo is contrary to our values and undermines our standing in the world," he wrote, "and it is long past time to end this chapter in our history."

Related: Obama's Last Full Day On Job Filled With Nostalgia, Thank You Calls

Obama didn't delve into his setbacks as president in his open letter to Americans. Instead, he asked people to continue to take part in their country — not just during an election year but during their lifetimes.

"And when the arc of progress seems slow, remember: America is not the project of any one person. The single most powerful word in our democracy is the word 'We.' 'We the People.' 'We shall overcome,'" Obama concluded. "Yes, we can."