The church has been preparing for the family since last year - before the congregation even knew who was coming or where they were from.
Smith, 59, and his wife, Katie, 60, have been working with Church World Services to bring the family over.
The agreement calls for the church to be responsible for the family - five people representing three generations - for a month.
"We have a moral commitment longer than a month," Smith said.
Until they are able to speak English and earn a living, the family members will live on property next to the church. For the past few months, church members have been collecting money and furniture to set the unit up.
The Rev. John Zsittnik said the church has been renting the property since purchasing it in June 1995.
Zsittnik said the congregation quickly rallied around the idea of sponsoring a refugee family after a church member suggested it.
"Someone came up with the idea and no one objected," he said. "It just felt right. It felt like God was leading us in that direction."
Church World Services has placed thousands of refugee families in American communities across the country, including a Bosnian family in Smithsburg a few years ago. Smith said the experiences elsewhere have encouraged Mt. Nebo.
Still, he said church members are under no illusions about the obstacles they face. Among other things, none of the family members speak English and none of the congregation speak Vietnamese.
Smith said he knows very little of Vietnamese culture and cuisine. He said church members will seek out Vietnamese translators and immigrants to help with the transition.
Fund-raising will be a persistent challenge as well.