A pastor and a legendary athlete are facing the biggest test of their lives.

They will be competing together with other elite athletes in what is probably the toughest contest known to man—the 2017 World Marathon Challenge, according to Assist News Service.

In this gruelling race set to start in Antarctica in January of next year, competitors will run seven marathons, a distance of 26.2 miles each, within seven days on all seven continents. That's running 183.4 miles over seven days in Antarctica, South America, North America, Europe, Africa, Asia and Australia.

All sorts of problems—jet lag between race venues, lack of sleep, extreme hot and cold temperatures, and fatigue—will subject the runners to extreme tests of their spiritual, emotional and physical strength.

But Pastor Matthew Barnett, 42, of the Los Angeles Dream Center, and Ryan Hall, 33, the American record holder in half marathons (59:43) and who has run the marathon faster than any American in history (2:04:58), are unfazed by it all.

Both from California, the two friends are joining the race for two different reasons.

Barnett is defying his doctors' advice against joining the race so that he could raise more money to better serve the homeless, addicted, and sex-trafficked people in Los Angeles. The Dream Center, which is facing financial challenges, has been providing help to people on skid row in L.A. since 1996.

For his part, Hall—who considers Bethel Church as his family's spiritual base—is viewing the race as part of his deeper quest for God. To him, the marathon challenge represents a second chance to run "God's way" free of the personal problems that led him to tell stunned sponsors, coaches and other professional runners that he was not joining the 2016 Olympic Games in Rio de Janeiro and leaving the sport this year.

Barnett wants to inspire people with his participation in the marathon. "I'm telling everybody who is facing seemingly impossible situations to face those things head on," he says.

"People who are in our rehab program are coming up to me saying, 'Pastor, I'm not going back to my addiction. I'm going to finish the program. If you can do this (the WMC), I can finish my program,'" Barnett says.

The pastor is in for the race despite his medical condition. In 2012, blood clots almost completely blocked both of his lungs. Although he was not yet a runner at that time, Barnett was told by his cardiologist: "It looks like you'll never run a marathon in your lifetime."

"When he said that, at the time, I had never run a marathon but something about those words—that something couldn't be done—stirred me on the inside.

"I said, 'You know when I get healthy from this, I'm going to run a marathon.'"

And he will, next year.