There a great line in Max Lucado's book 3:16 The Number of Hope that is worthy of a bit of discussion. Max is talking about being born-again or the new birth of John 3 and he writes, "New born heart are born of heaven. You can't wish, earn, or create one. New birth? Inconceivable. God handles the task, start to finish" (6).
That's it. You didn't miss it…did you? God handles the task, start to finish.
The psalmist said like this over and over—Salvation is of the Lord!
I am completely and fully dependent upon God for every aspect of my salvation. There isn't anything I can do to earn it—it is purely an act of grace of God's behalf—Start to finish. I don't begin it and He finishes it.
God is not dependent upon me to save a soul—clearly he used preaching, but he doesn't have to and when he uses preaching it is him using it from start to finish.
In and of myself I have no ability to say something, play something, or even sing something to get someone to respond to the gospel.
I strongly in the vast majority of the times when someone is responding to an invitation to get said the person walking down that aisle during an invitation is already saved. Those steps are God-initiated, God-ordained, God-strengthened steps and the person taking them is a new creature in Christ.
The natural man doesn't respond to spiritual things—it takes a heart filled with faith from the Holy Spirit to respond and this is why we must confess over and over again—salvation is of the Lord.
Thus there isn't any aspect of man's salvation that competes with the glory of God—both faith and repentance are both presented as gifts in the Acts of the Apostles.
If I have loved one, friend, relative, companion, co-worker or neighbor for which I am concerned that they are not born-again—the most important thing I can do is to pray to the Lord of salvation that He would send the Holy Spirit to give them faith and repentance.
So my prayer will be over and over again, "God the Father draw them to your Son in Jesus' Name!"
Will I witness—YES absolutely—but my witnessing is completely dependent upon God-the Holy Spirit showing up—so my prayer time will be exclusively focused upon my theological perspective that salvation is a God-thing from start to finish.
I must completely and fully rest in the promise of Phil 1.6 that He which has begun a good work will perform and complete that same good work until the day of Jesus Christ.