In brief, from Abu Daoud (he links to the full article from Mission Frontiers):

1. A sure salvation
2. Jesus
3. A Holy Book: the power of the Bible
4. Then you will know the truth (Christianity teaches the truth about God, humanity and ethics)
5. Dreams and visions (you can find out more about that here)
6. The love of God manifest in Christ and the Church
7. I have called you friends: relationship with God
8. Persecution (both being persecuted and seeing others persecuted)