According to Christian belief, something out of
the ordinary happened to Paul, the emperor Constantine,
and the writer Augustine that made them become
believers in Christianity. Write three sentences comparing
their experiences.

=> The three of them that is Paul, the emperor Constantine,

and the writer Augustine met with Christ(Although not Physically).

=> Paul saw a bright light and heard a voice.

=> Emperor Constantine saw the sign of the Cross in the sky.

=> writer Augustine heard a voice.

Explanation:

Paul(formerly Saul) met with Jesus Christ on his way to Damascus(with mission of bringing Christians to Jerusalem and locking them in prison). You can get the full story of how Paulet Jesus in the book of Acts, chapter 9 verse 1–22. After Paul encounter with Jesus he travelled far and near to spread the Gospel.

The emperor Constantine is known and recorded to be the first Emperor in the history of Roman Empire. The emperor Constantine saw the sign of the cross in the sky.

Writer Augustine was not of Christianity before until he converted after hearing a voice telling him to read the Bible.