Gibbon’s fun to read but so wrong in so many ways beginning with ascribing Christianity as a cause of the “fall” - saying that Christianity caused the decline and fall of Rome by undermining the faith of the people in paganism (official religion), adn thus undermining the state apparatus which that religion supported and blessed.
So Gibbons is a fun read but so wrong and narrowly illogical in so many ways.
Religion had nothing to do with the Fall of Rome. Notwithstanding all the other signs of decline, the most fatal defect was Rome's failure to solve the problem of succession. Every time an emporer died there was basically a free for all for power, which sometimes even resulted in multiple "emperors."
The way I interpreted Gibbon’s statements about Christianity is that it, unlike the “old” pagan religion of Rome, emphasized the promise of life after death. In that sense, the Romans could disregard problems and hardships on earth since they would be set right in the next life.
In other words, the old Romans worked harder at maintaining the world they lived in because it was all they had.