Imaan Rises and Falls

In a nutshell
Faith increases and decreases, and what that means for ordinary life.
From the Qur'an
To be added: verse text, translation, surah and verse number.
From the Sunnah
To be added: hadith text, translation, collection, number and grading.
In simple words
To be written.
Common misunderstandings
To be written.
What to take away
To be written.
References
To be added.
Editor notes (remove before publishing)
Planned anchors, to verify when collecting: Qur'an 8:2, 9:124, 48:4, 74:31; hadith on renewing Imaan (check grading)