Reasons you should go on mission:
1. Matthew 28:19-20, "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age."
That's it. The only reason you need.
Matthew 28:19-20 is what Christians recite as the "Great Commission," and it is where Jesus bluntly tells us to go. Honestly, if you're a Christian, you shouldn't really need any other reason to go on mission than this verse, especially overseas. We should simply go because Jesus told us to go. It's really pretty simple. Jesus plainly tells us to go, to all of the nations, and make disciples. There isn't really room for much confusion or questioning. You're scared to go? Good thing Jesus plainly says He will be with you always to the "very end of the age." You don't know what to do when you get there? Make disciples, baptize, teach the Bible. You don't know where to go? Go to all of the nations. Everyone needs to hear. Don't seclude any nation, people, race, etc. The Great Commission leaves no excuse or reason to not go. We are all called. We don't need to sit around and wait for some flashing sign or for every little thing to fall into place before we commit. God will work out the details. We just need to go and we need to go now, because people are starving, suffering, dying, being sold into slavery, worshipping plastic and wood, and much worse–without ever even knowing about Jesus.
Here's the thing too with missions and going: You gain much more than you give. Should this be you're reason for going? Absolutely not, but it is something that has always happened as a byproduct of being obedient in my experience. The people I have worked with and the relationships that I have built have done more in my life and heart than any food or items I gave out or building I helped build have probably done for the people I served. The people I have met along the way in my travels and the things I've seen God do have helped shaped me into who I am and my outlook on life. It's taught me so much more than anything I ever expected when I signed up.
Out of all of my experiences with missions, though, one thing I have learned no matter where I have gone is that you come back changed. Your worldview widens, and you see that there is a world out there that is so much bigger than yourself. You see how big God really is. Let me tell you there is nothing greater, in my opinion, that shows how big God is than hearing people of a different nation worshipping God in their own language. I think in America we sometimes put God in a box and limit His abilities and even ignore Him. It's humbling to see that God is much bigger than the four walls of our local church and is actively moving and doing.
You also come back discontent, which is not a bad thing at all. As Christians, we should be discontent with our comfortable lifestyles when so many others are hurting and screaming for help. We should be discontent that American Christians won't leave our iPhones, or beds, or social media, or Netflix to go serve someone who lives a lifetime without any of the things we leave behind for a week. We should be discontent that we live in a culture that always asks for more when we have more than enough and then some. We should be discontent that American Christians won't even drive to a church for two hours out of their week because it's raining, when people in third world countries are walking barefoot in the brush for literally ten miles in clothes they've had on all week just to go to church, and they do it with a smile and eagerness. We should be discontent with the fact that we are doing really well and considered dedicated if we pick up our Bible once a week, when people in other countries literally guard the Bible with their lives and flock to it in masses when they finally get it in their country where it's illegal. We should be discontent and we should be different when we come back. We should not ignore the broken and helpless. We should not put ourselves and our comfort before what God has plainly told us to do. We should do something. We should go.
P.S. "God doesn't call the equipped, He equips the called." You'll be alright.