By Daniel Burke and Ashley Fantz, CNN

(CNN) - It wasn’t as if God's voice boomed through sun-parted clouds, telling Kent Brantly to move his family to Liberia.

Still, the young doctor said, the call was clear.

It echoed through the congregation where he was raised, Southeastern Church of Christ in Indianapolis.

Standing before the church community in July 2013, months before he left for Africa, Brantly said he heard the call in the teachers who urged him to memorize Scripture and the neighbors who funded his first mission trip years ago.

He saw it in the aunts and uncles who spent their vacations running Bible camps, organizing youth groups and serving missions themselves in Africa.

“It may not seem like much,” Brantly said in an emotional address to the Southeastern congregation, “but when you connect the dots you see a grand design that God has used to draw my life in a certain direction.”

For Brantly, that meant serving a two-year medical mission in Liberia with Samaritan’s Purse, a Christian relief organization. But in a grim twist that garnered international headlines, the 33-year-old contracted Ebola while treating patients and was airlifted back to the United States.

Brantly and a fellow missionary, Nancy Writebol, who was serving with SIM, another Christian aid organization, are being treated for the disease at Emory University Hospital in Atlanta.

After Liberia's outbreak began in March 2013, Writebol volunteered at a hospital in Monrovia, where she disinfected doctors and nurses working with patients stricken by the disease.

Despite their weakened health, their trust in God remains strong, family members said.

“Mom is tired from her travel, but continues to fight the virus and strengthen her faith in her Redeemer, Jesus,” said Jeremy Writebol, Nancy’s son.

On Friday, Brantly said that he felt a spiritual serenity even after learning his diagnosis.

“I remember a deep sense of peace that was beyond all understanding,” he said. “God was reminding me of what he had taught me years ago, that he will give me everything I need to be faithful to him.

Though Brantly's wife and children had been in Liberia with him, they had returned to the United States when he became ill.

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