What is the reason for the fluctuation in the feeling of the sweetness of faith and acts of worship? Is that due to sins, and how can they be avoided?

Tasting the sweetness of obedience and the pleasure of faith is a great blessing. This sweetness is taken away from the servant by slackening in obedience, indulging in worldly pursuits, and committing sins. Sins remove blessings, so the servant must be keen on preserving this pleasure and investigate the reason for its disappearance. If it is a shortcoming, he should abandon it; if it is heedlessness, he should rectify it through remembrance (dhikr); and if it is a sin, he should offer sincere repentance. What helps in avoiding sin is to recall its ugliness and its consequences, to read the book "Ad-Da' wa ad-Dawa'" (The Disease and the Cure) by Ibn al-Qayyim, to strive in supplication, to remember Allah, and to keep the company of the righteous.