I believe the quote indicates that you must stay strong and stay on the right path. The part stating "Every saint had a past..." possibly means that there is a reason they are angelic. They could have learned from mistakes in the past and changed their ways to good. The part stating "Every sinner had a future..." indicates they already blew their chance away with negative actions. Therefore, their future shall be negative. To prevent this, be like the saint and learn it's okay to make mistakes--just don't repeat them.
