The pews of the 12,000-seat auditorium are packed for Sunday services and the capital's skyline is aglow with red neon crosses. Those not inside the Yoido Full Gospel Church -- the world's largest congregation -- can watch the sermons online in 16 languages.
South Korea has an ancient tradition of Buddhism, but in recent times evangelists have put Christianity on track to becoming the nation's dominant faith. Korean missionary work, second only to the US, places it at the forefront of the global search for converts.
But the kidnapping of 23 church volunteers in Afghanistan on July 19 is forcing churches to think again.
In recent years, hundreds of volunteers have been expelled from Afghanistan, Egypt and China, while others were detained or killed in Iraq. Some press ahead in Somalia, even though it was declared off-limits by the Korean government.
Two of the hostages in Afghanistan -- a clergyman and another man -- have been shot to death and abandoned by the roadside. The fate of the remaining five men and 16 women, remains uncertain.
The church and the hostages' relatives say the volunteers were working on humanitarian projects and were not evangelizing.
They are mostly in their 20s and 30s, and belonged to the Presbyterian Saemmul Community Church, which has roughly 3,800 followers, in the town of Bundang just south of Seoul.
Many attended Bible school together and trained as nurses, teachers, musicians, engineers and even a hairdresser before setting off to Afghanistan on a trip headed by a pastor with the Korean Foundation for World Aid, a non-governmental agency guided by Christian beliefs.
There were 16,616 South Koreans posted in 173 countries as of January, according to the Korea World Missions Association.
The country's recent embrace of Christianity, once a tiny minority, has spurred one of the most dramatic national religious shifts in the last century. It now equals Buddhism at around 26 percent out of a population of 49 million, according to conservative estimates. The remainder have no stated religious affiliation.
Americans successfully introduced Christianity to Korea 120 years ago, but it has really gained a foothold since the 1960s, after 35 years of Japanese occupation and the 1950-1953 Korean War that left about 2 million Koreans dead.
South Korean missionary work is driven by a sense of postwar moral debt to the foreign missionaries who built schools, hospitals and orphanages. The church won further support for helping bring democracy to South Korea in the 1980s.
Christian groups also provide extensive humanitarian help to neighboring North Korea, as well as its citizens who flee into China to escape Kim Jong-il's dictatorship.
At US theology centers, Korean missionaries are trained to work in potentially hostile environments by teaching culture and language rather than preaching.
"Many [Korean] ministers, theologians, and seminary professors have been educated in the US," Sung-deuk Oak, an assistant professor of Korean Christianity at UCLA, said. "American theology is powerful in Korea."
Cross-culture church planting, as it is known in Christian circles, has become "a worldwide trend" that is popular at Korean's dominant Presbyterian Church, he said.
South Korean missionary work targets a geographical region of the northern hemisphere, known as the "10/40 window," between 10 and 40 degrees north of the equator, said Pastor Oh Sung-kwon, Secretary General of the National Council of Churches in Korea.