What is the interpretation of a committed person's feeling that they have gained the world and are safe from sins, while continuing to fall into them? And does that diminish their faith, despite the pleasure of commitment not fading away?

The doctrine of the People of the Sunnah and the Community is that faith increases with obedience and decreases with disobedience. Therefore, falling into sins or shortcomings in worship may weaken faith, and upon one is repentance and renewal of faith through the remembrance of Allah and contemplation of death. Faith has a sweetness and delight that the believer feels, as stated in the Hadith: "Three qualities, whoever has them, will find the sweetness of faith: that Allah and His Messenger are more beloved to him than anything else, that he loves a person only for the sake of Allah, and that he hates to return to disbelief as he hates to be thrown into the Fire." As for the pleasure of sinners, it is not from the sweetness of faith, for some people have their evil deeds made appealing to them, so they see them as good, and thus go astray.