Reading The Book
And they were not commanded except to worship Allah , [being] sincere to Him in religion, inclining to truth, and to establish prayer and to give zakah. And that is the correct religion. [Al-Quran 98:5]
Mission of the Messengers-XXXIX
Disease & Cure - XIII
The Quran is a guidance for all humans, but who takes what guidance from it, and when, varies from individual to individual. Most humans have a tendency to become less religious, or even abandon it, when they are in a state of prosperity, or even when opportunity presents itself. Swarming locusts are solitary grasshoppers who change physiologically when the environmental conditions and population densities are favourable for swarming behaviour.
Surah at-Teen informs us that humans were created excellently, and then returned to the lowest of the low. Yet, there is hope for those who believe and do reformative deeds for an uninterrupted reward.
The Quran also contains cure for the believers. However, the same causes loss to the unjust!
The Quran is meant to be recited in the contact prayers, and Surah al-Muzammil specially advises night vigil for protection during the end times.
Surah az-Zumar extensively discusses sincerity in The Deen.