Luke 1:3-4 (ESV)
it seemed good to me also, having followed all things closely for some time past, to write an orderly account for you, most excellent Theophilus,  that you may have certainty concerning the things you have been taught.
Luke wrote his Gospel so that Theophilus might have certainty concerning the things he had been taught. It is never a waste of time to take time to help believers come to a better understanding of the truths of the Scriptures. It is never wrong to spend time with people so that they are less riddled with doubt about the truths of the Gospel and the Christian life. We do not know if Luke had any idea about how far reaching his Letter to Theophilus would become. But we do know that he wrote it to solidify the faith of one man.
I meet with a man every Wednesday morning and another on Wednesday afternoon, one early Thursday evening and two more later that night. It is tiring and sometimes I wonder if I am accomplishing anything of value at all. This little introduction to Luke’s Gospel helps put things into perspective. Luke was writing to bolster the faith of one man. God, in His providence saw to it that it reached many more people than that one man. But writing it for that one was not a waste of time. And if the only audience Luke’s Gospel had ever had was Theophilus, it still wouldn’t have been time wasted.
1)We do not know how far reaching our acts of obedience will be taken by God. Our duty is to obey. Do not try to build an empire or a ministry. Give yourself to obedience to the call of God and let Him do with it as He sees fit.
2)If all God gives you is one person to influence do not bemoan the fact that you do not have two or two-thousand. Thank God for the one and pour your whole heart in doing for that person all that God enables you to do. Be faithful, not ambitious.
3) Always minister to those God has given you as if they weer the most important people on the face of the earth, because as far as you are concerned, they are. This is the field God has called you to minister in. Do not sell it short. Do not give it less than your best simply because it is small or different from what you thought or wanted. Whether those you serve ever turn out to be great movers and shakers is not your concern. Simply do as you are called to do and God will do what only He can. There is no better system than that.
Serve Him faithfully, regardless of how well it fits in with what you had envisioned for yourself. Ultimately, you will not be disappointed.