You can sum it up in one word: access.
While there are many unbelievers in the US there are innumerable churches, Christian ministries, magazines, television and radio programs, even entire stations, plus thousands of pastors and, of course, other Christians to reach the unbelievers. Over 1 out of every 4 full time Christian worker in the world lives and serves in the United States.
On the other hand, in many nations there is no, or very limited, access to the gospel – not on television, not on radio, no churches, no Christian publications, absolutely no way to discover who Jesus is. It is estimated that in some areas of the world there is only one Christian worker (a pastor, lay leader, missionary, etc) for every 1 million people.
One missionary, upon entering a village thought to not have any church or access to the gospel, began to talk to a woman about Jesus. The villager thought perhaps a “Jesus” was a brand of sewing machine.
It is sadly true that there is an abundance of non-believers in the United States but there is also an abundance of believers who can easily make Christ’s name known. There are an endless number of opportunities for a seeker to discover who Jesus is and the message of salvation. A question that arises then is: Shouldn’t everyone have an opportunity to hear the gospel at least once?
Finally, if the facts don’t make a case for sending foreign missionaries, surely Jesus’ command does. He tells us to go into all the world (Matthew 16:15). We are to go to Jerusalem (or own city), Judea (the surrounding area), Samaria (our neighbors – even if they aren’t very friendly toward us) and the ends of the earth (Acts 1:8). It is not a one-or-the-other option. He said we were responsible for local and global, Jerusalem and the ends of the earth. Obedience demands we send missionaries. Are you ready to go?