You may be the person whom God uses to reach someone who will, in turn, change the world.
Plant your seed in the morning and keep busy all afternoon, for you don't know if profit will come from one activity or another—or maybe both (Ecclesiastes 11:6).
Saul, later to become the apostle Paul, was doing the work of the kingdom before he was even in it. Had he not persecuted the church, I think the first-century Christians probably would have been content to stay in their little holy huddle in Jerusalem and never leave town. It was great, God had blessed, and there were believers all around. So who wanted to leave Jerusalem? But with Saul's persecution, the Christians were forced to spread out, and in the process, they took the gospel of Jesus Christ to the world.
I think the person who probably had the greatest influence in bringing about the conversion of Saul was Stephen, the church's first martyr. I believe it was Stephen's bold testimony that actually threw fuel on Saul's fire, because Saul was under the conviction of the Holy Spirit. Stephen didn't have a long ministry. He never wrote a book of the New Testament. But if his only convert was Saul of Tarsus, then he was one whopper of a convert.
You may not reach millions. You may not reach thousands. You may not reach hundreds. But you may be the person whom God uses to reach someone who will, in turn, change the world. Or, it may be a child whom you raised in the way of the Lord who reaches someone else who talks to someone else and eventually shares the gospel with someone like Saul. So here is what you need to realize: it's not over till it's over.
We need to be faithful in sowing the seed of the Word of God, because we don't know where that seed will go... in this life... or in the next generation... or in the next one.