Pray for them until five days after they are graveyard dead.....
Your minister at church is confused or congusing you. While Jesus told us not to use vain repetitous words when we pray, he gave us an example of what you are talking about here:
What your pastor is talking abou us using vain repetition in an individual prayer. Asking the same thing over and over in a single prayer, and usually to be noticed.
And by the way, you could do that minister a favor by pointing this out to him so that he does not give that advice to others.
It is perfectly ok to literally bug God for something that important.
Just remember that it is not Gods decision whether or not a person comes to Christ that individual person has to make that decision........ so don't stop asking that person yourself to go along with the prayers.
Thank you so much for the scriptures and to everyone else advice. I will continue to pray for the person in question.