What subjects would you want to cover if you were the one on THEIR door step?
If you mean " What subjects would you want to cover if they were on YOUR door step?" then I would try to say the following:
Some Christians visited me years ago and offered to help me understand the Bible. I listened to them.
I gave so many years of my life to spreading the message of Christ's Kingdom that THEY taught me.
Now, I realize that those years were wasted, the message was false.
If you haven't already found out why former members of your belief have left, you need to do so.
I now understand that the Bible can be twisted in ANY way, to suit ANY goals of ANY group.
I won't be referring to it with you. I will keep it to myself, have a nice day.