Don't kill yourself over yourself over if it IS God's plan or NOT most of the time God wants us to be faithful and to LIVE out our faith wherever we are. Its easy to get in the "what does God want me to do thing" When really its about your heart.
33To love him with all your heart, with all your understanding and with all your strength, and to love your neighbor as yourself is more important than all burnt offerings and sacrifices."
Mark 12:33
so basically we need to be careful not to do things for God but rather do things out of our RESPONSE to God's love and grace. This includes serving! If God really wanted you to serve you would KNOW without a doubt but honestly what if God wanted you to serve and then you thought in your heart that He didn't want you to? Then you went agianst God's plan? Um "listening" to God's voice is actually not 100% right because when you "listen" your really just struggling with issues in your heart and The heart is deceitful above all things and beyond cure. Who can understand it? Jer. 17:9
On a side note can you better discern what is deceitful and what is not? Yes! by filling it with the Word and through the Holy Spirit but even then its still sketchy!
So I don't think the question is: "Does God want me to serve in this particular area?" its more like "I have this opportunity to serve will I do it 100% with everything that I have because of what God has done for me?"
Take Paul for example
there were times when God did tell Him SPECIFICALLY where to go and preach
but how about the other 90% of the time?
Paul just went to preach the gospel in faith and as He acted in faith God opened up doors for His Kingdom to be established.
In fact if you read near the end of Acts theres a point where He is warned "through the Spirit" not to go to Jerusalem but then decides to because he felt a huge burden there and afterward the Holy Spirit tells him whats going to happen.
God is ALREADY working. The question we should ask is "How can I be a part of what He is already doing?"
So man do God's work (sharing gospel) in faith and ministering to people in faith.
