How can one avoid disobeying his Lord and preserve his faith so that he may have a good end, and how can he differentiate between self-talk and the whisperings of Satan?

As long as a person breathes, they must beware of a bad ending (of life). However, if one performs righteous deeds, holds oneself accountable, and avoids evil, then one should have a good opinion of their Lord and maintain a balance between fear and hope, for Allah has praised His servants with this characteristic.

Among the ways to preserve faith are: reducing sins, and repenting and seeking forgiveness. For by repentance, Allah erases sins, and the one who repents from a sin is like one who has no sin. Seeking forgiveness and supplicating with hope are among the reasons for the forgiveness of sins.

Among the means to preserve and increase faith are: seeking beneficial knowledge, reciting the Quran with contemplation and reflection, moistening the tongue with the remembrance of Allah through both absolute and prescribed invocations, and keeping good, believing company, for Satan is with the solitary and further away from two.

And know that Allah does not hold a person accountable for inner thoughts (حديث النفس) unless the servant acts upon them. And whispering (وسوسة) is from Satan; if the servant repels it, it has no effect. Accountability is for being swayed by it and acting upon its dictates.