Are trials and tribulations a punishment for a believer's past sin?
No. For the believer, trials and tribulations are not punishment for past sin. The bema seat is not a judgment for sin; it is where believers appear, and the issue there is not sin. If you are saved and a child of God, you should not think you still carry sin on your back.
Les explains that the word often translated judgment is bema in Greek, a raised platform. He notes it was also used in the Olympic games for the judges who determined first, second, and third, and Paul is more apt to have that analogy in mind than a political bema seat. The bema seat is not for judging believers for sin. Les says many people over the years have asked if they are going through trials and tribulations because of sin in their past. He first asks them, Are you a believer? Are you a child of God? If they know they are saved, he challenges the idea that they still have sin on their back.