The words of the Holy Demon are precisely the 'nature' and 'reasons' that the Heavenly Demons intend to lure people into corruption. When the Heavenly Demon transforms, the first to fall are the most vile, the weakest, and those with the most unsteady Dao Heart. The demons they transform into will be quickly slain, and might not even be regarded as demons, but rather as similar to Deviation, with evil thoughts entering the body.
And the thoughts of the Heavenly Demons would also be influenced by the stupidity and vile nature of these people, hence, the early Demon Calamities are easiest to deal with.
However, if a cultivator with a sufficiently steadfast Dao Heart and strong mind becomes fallen due to accident or other karmic reasons, then the situation becomes completely different.
