An old friend asked me some questions about mission work and such via email, and I figure excerpts of it might be of some interest, so here they are.
My motivation started back when God first saved me around age 15 1/2, actually. I have since that time been very interested in missions and overseas work. Almost went to Albania one summer with Teen Mania, but I think I was too chicken, so I didn't do it. So that conviction and that direction of my heart and desires has stayed oriented that way, and I also love foreign languages and being a foreigner, so that's something else God has used to hold my interest in overseas work.
Biggest challenge for us was definitely letting go of our relationships in the US and also entrusting God with all the unknowns about moving to a diff country and hoping and praying to find believing fellowship there. As it turns out, we DIDN'T find much of any believers where we were in Japan, but God sustained us anyway. God used that time to change me an awful lot.
The 1st time, in France, He taught me about His sovereignty over the world mostly. I had spent a summer in nervous spiritual preparation b/c I knew that France was known as the missionaries' graveyard and that it was a dark place. So I thought that one magically loses one's faith when one goes to a place like that. Of course, that's not the case at all - one falls into a missionary graveyard b/c one does not concentrate on personal holiness, obedience, reliance on God, and has unreasonable expectations (such as thinking that thousands will fall down in repentance within a month of your starting to preach and that you'll head a megachurch). And God taught me about His overseeing of ALL nations and their ideas - the French have half-formally enthroned Reason as their god, and God showed me the wrongness of that.
In Japan He taught me about His provision, His sovereignty over MY life, and being bold to introduce the Gospel to people early on in conversations. Provision - we were the only Americans, w/ a low level of Japanese, on an isolated island in the middle of the ocean. Aubrey miscarried our first child while there, and God orchestrated an amazing sequence of events to get us off the island and to the hospital on the other side of the next island over from where the airport was, and an expert interpreter to help us, and on and on. Sovereignty over my life - my plan was to stay in Japan for multiple years and learn Japanese really well and from there move on to either full time missions in Japan or onto some other country or whatever. God brought us back to the US after only one year, and that has been perhaps the hardest action on God's part that I've ever wrestled with. The proverbial late nights of prayer, running out excess stressed energy, pacing back and forth, wringing hands, yelling at God, prayer at the beach in the middle of the night AND yelling at God at the same time, struggle, resignation... I went thru it all! Then much more when we did get back. Crazy. But God is using us here. I knew He would, but it's hard to figure that He'd prefer us to be here rather than overseas, especially given the way that he's made our hearts to love internationals.
At the end of my time in France, I visited a friend who was volunteering at the Wycliffe institute NW of London and was vastly impressed by their installation and what I saw. I have since thought it would be grand to work for them, and of course their vision is highly praiseworthy - get the Bible into the hands of (usually illiterate) people groups who don't have the Bible in their own language.
So I'd say to try to spend some time watching the way the agency does their bizness and whose vision fits with yours. I'd urge you to keep the main priorities the main priorities. That is, all the clean-water wells, microloans, medical supplies, and food shipments are meaningless where the Gospel is absent. Will the Lord find blameless he who gives temporary, perishable provision and intentionally withholds, whether out of fear or embarrassment or whatever, his most precious possession - the saving message of the Gospel of Christ?