Martin Luther was once approached by a man who enthusiastically announced that he'd recently become a Christian. Wanting desperately to serve the Lord, he asked Luther, "What should I do now?" As if to say, should he become a minister or perhaps a traveling evangelist. A monk, perhaps.
Luther asked him, "What is your work now?"
"I'm a shoe maker."
Much to the cobbler's surprise, Luther replied, "Then make a good shoe, and sell it at a fair price."
In becoming a Christian, we don't need to retreat from the vocational calling we already have—nor do we need to justify that calling, whatever it is, in terms of its "spiritual" value or evangelistic usefulness. We simply exercise whatever our calling is with new God-glorifying motives, goals, and standards—and with a renewed commitment to performing our calling with greater excellence and higher objectives.
One way we reflect our Creator is by being creative right where we are with the talents and gifts he has given us. As Paul says, "Each one should remain in the condition in which he was called. So, brothers, in whatever condition each was called, there let him remain with God" (1 Corinthians 7:20,24). As we do this, we fulfill our God-given mandate to reform, to beautify, our various "stations" for God's glory–giving this world an imperfect preview of the beautification that will be a perfect, universal actuality when Jesus returns.
I once heard Os Guinness speak about what such reform will require. He said the main reason we aren't making more of a difference in our world is not that Christians aren't where they should be, but that they aren't what they should be right where they are.
So, you're free to stay put, right where you are.