"So, what is your calling?"
Missionaries are trained to answer this question on command. They will answer something like...
"God has called me to China!"
"To children e v e r y w h e r e!"
Quick answers summing up the goal and focus for the rest of their life.
For me it's even more simple. Instead of asking me to commit my life to a specific country, God has asked me to commit my life to Him. We have all heard that life is a journey, but where is that journey taking you? My life journey is nothing more than falling more and more in love with God, and letting the rest of my life be an overflow of that love.
No seriously, that's it.