In preparing for their second missionary tour, Paul and Barnabas had a decision to make – to take John Mark or not (Acts 15:36-41). God did not tell them what to do, and they ended up making opposite choices. Which one was right? Later Paul realized that his estimation of John Mark may not have been totally accurate (2 Timothy 4:11), but this is not to say he made the wrong decision. Two missionary teams going to two mission fields doing twice as much missionary work surely demonstrates that neither decision was wrong. The Lord allowed Paul and Barnabas to make their own choices, then he made sure that both decisions worked together for good.
To be a missionary or not to be a missionary? I was told multiple times in preaching school, "If you can do something other than preach, do it" (cf. Batsell Barrett Baxter, The Heart of the Yale Lectures 6-7). The point is that you should only be a preacher if your conscience will not allow you to do anything else. The same is true of missionaries. It is not a matter of prestige, adventure, love of travel, guilt, or any other questionable motive. The bottom line is whether or not you can be comfortable doing something else. But if you carry in your heart the burden of a lost world and you have a fire burning in your bones and you can’t rest knowing that you have an untold message that has the power to save souls, then your choice ought to be clear. Paul expressed it this way: ". . . compulsion presses hard upon me; yes, woe is me, if I do not proclaim the gospel" (1 Corinthians 9:16, McCord).
The desire to be a missionary, however, is not the only consideration. There may be some who have the aspiration but lack the fundamental people-skills, adaptability, tenacity, or other qualities necessary to be an effective missionary. While at least some of these traits can and should be developed, until then those who lack them may be better suited for other areas of service. An ill-equipped missionary can sometimes do more harm than good.
How, then, do I determine whether or not I am suitable for the challenge and how do I go about identifying and eliminating any possible inadequacies? The best place to start is where you are right now. Get involved in the work of your local congregation, which usually requires more than just waiting to be asked. Be evangelistic – share the gospel with the unsaved people in your life right now. Take advantage of campaign opportunities, both local and abroad. Read books and articles about missionaries and missionary work. Correspond with or talk to current and former missionaries. Most Christian universities and some other church-affiliated schools offer courses in missions, cultural anthropology and evangelism, and some even coordinate missionary apprenticeship programs. Above all, be a diligent student of God’s word. Good personal study habits are indispensable. You may even consider attending a tuition-free preacher training school to enhance your study skills and increase your Bible knowledge.
While much experience can be gained by serving the Lord at home, to a large degree the only way to fully prepare for foreign missionary work is to actually do it. There are some things you just can’t learn from a book, in a classroom, or in another unrelated environment. No matter how prepared you think you are or you think you need to be, most of your learning, growing, and maturity will develop on the mission field. There comes a time when you must step out in faith, take your tiny seeds of knowledge and limited experience, and venture into the exciting, challenging, faith-building world of cross-cultural evangelism. "Also I heard the voice of the Lord, saying: ‘Whom shall I send, and who will go for us?’ Then I said, ‘Here am I! Send me’" (Isaiah 6:8 NKJV).
–Kevin L. Moore
*Adapted from my book The Single Missionary  6-13.
Related Posts: Called to Be a Missionary Part 1, Part 2, Counting the Cost of Being a Missionary Part 1, Part 2, My Life as a Missionary