Saeed Abedini, who was born in Iran and whose family home is now in Idaho, relayed the letter of gratitude through his father during one of his sanctioned weekly 20-minute visitor sessions.
"Thank you again for standing up for my family and I and for thousands of Christians across the world who are persecuted for their faith in Jesus Christ," Abedini wrote.
In 2009, Abedini was arrested in Iran and later released after formally pledging to stop organizing churches in homes. He returned to Iran in 2012 to help build a state-run secular orphanage. It was during this visit that he was abruptly pulled from a bus and imprisoned.
Over the last two-and-a half years, Abedini has endured beatings and torture at the hands of his jailers and fellow inmates, according to his family. At one point, reports circulated regarding death threats targeting Abedini from ISIS prisoners held at the same Iranian facility.
"President Obama, you have my prayers from inside of these walls," Abedini wrote. "I pray for God's guidance, wisdom and blessing for you as you lead this great nation."
Abedini's letter to Obama was posted online by the American Center for Law and Justice (ACLJ), an organization founded by television evangelist Pat Robertson that has worked to publicize Abedini's situation.
In the letter, Abedini thanked Obama for meeting with his wife, Naghmeh Abedini, and their children in Boise, Idaho on January 22.
"They have had a heavy burden to carry in my absence, and your presence helped to relieve some of that burden," Abedini wrote.
"With this meeting I feel more hopeful now; it's becoming a higher priority," said Naghmeh Abedini. The 10-minute face-to-face meeting with the President was "an answer to my prayers," she added.
"The meeting took place in a personable and intimate setting. The kids were there and I saw a lot of compassion and care as we talked," Naghmeh Abedini said. The Abedinis have two children, Rebekka, and Jacob, both under the age of 8.
Jacob asked Obama if he would be able to bring his father home in time for an upcoming birthday, according to the Abedini family. Sharing some words of comfort, the President responded that he would try.
"I could see that he cared as a father," said Naghmeh Abedini.
During their meeting, the President reassured Naghmeh Abedini that her husband's case was a high priority. He told her that he and Secretary of State John Kerry meet regularly regarding the issue, and Kerry continues to bring up Abedini and to push for his release in ongoing meetings with the Iranians.
Naghmeh Abedini said Obama promised her the United States will "keep at it until Saeed is released."
The Abedini family has been fighting for his release for the last three years.
Earlier this month, the Obama administration called for Abedini's immediate release, along with other Americans held in Iran, including Washington Post Tehran Bureau Chief Jason Rezaian.
In a subsequent briefing, White House press secretary Josh Earnest emphasized that the issue of American citizens imprisoned in Iran is of great concern for the administration. The fact that Kerry raised the issue in his diplomatic exchanges with the Iranians "is an indication of how seriously the United States takes this case," said Earnest.
Abedini continues to be denied adequate medical attention for injuries, said Tiffany Barrans, International Legal Director for the ACLJ.
"It's not that they haven't given him any treatment. It's that they continue to give him medications that have not helped and doctors' medical tests have concluded surgery is necessary," Barrans said.
Despite their grueling emotional journey, Abedini family members say they continue to hold on to hope as they make headway in bringing increased attention to Saeed Abedini's story, both in the United States and internationally.
Since meeting the President, Naghmeh Abedini said she has received follow-up calls from the White House and is set to meet with U.S. Ambassador-at-Large for International Religious Freedom David N. Saperstein at the end of February.