(This article was published on John Piper's blog, and I have put a snippet here to encourage people to read the article in it's entirety. To read this entire article – only one page – click on the link at the bottom of the post, or on the photo above.)
I was never called to be a missionary, nor was I drafted. I volunteered. No special call was needed. I chose to go; I wanted to go; I was compelled to go. And where I go is always determined by an open Bible and a stretched-out map of the regions where Christ is still unknown and un-praised!
I chuckle when I hear missionaries and pastors talk about “surrendering to the call” of ministry. I always want to ask, “After you surrendered, were you water-boarded, or just hauled off in handcuffs and leg irons.” Was it really necessary for you to be abducted by a heavenly vision before you would go into the work of the gospel?
http://www.desiringgod.org/blog/posts/dont-complicate-the-missionary-call