They are always fearful of the interference of Satan because...
They are always fearful of the interference of Satan because he keeps trying to divert them from worship of Allah (S.w.T.). May Allah (S.w.T.) give the vision to people that they are able to understand if the acts they are doing are really good or are evil acts that Satan has tempted them to perform. It is the common observation that an act appears good and harmless but in reality it turns out to be otherwise. To illustrate the point a tradition is mentioned here.
Satan Praying Suspended in the Sky It is mentioned in Bihar al-Anwar from Usūl al-Kafi that Imam Ja’far as-Sadiq (a.s.) narrated about a person, in the olden times, who kept himself busy in prayer and supplication to Allah (S.w.T.). He was so deeply engrossed in prayer that Satan, despite all the efforts, was unable to disrupt this activity. Upset at his failure, Satan called a meeting of his retainers to devise ways and means of achieving his desire.
He said: “I have not succeeded tempting the pious person despite all my efforts. Can you think of a stratagem to unnerve him”? One of his disciples said, “By creating evil desires in his mind I shall motivate him to commit adultery.” Satan replied, “There is no use. The desire for women has been extinguished from his heart.” Another disciple said, “I shall tempt him with delicacies and drinks that he gets destroyed consuming Haram food and alcohol.” Satan said, “No use!
After years of penance he has lost palate for good food.” A third retainer said, “Perhaps he can be tricked through the way of prayer which is his favorite activity!” Satan said, “Yes. We might succeed this way.” Anyway, the result of this confabulation was that Satan himself took the responsibility to do the job. He adopted the garb of a human being, suspended himself in the atmosphere sitting on a prayer mat and pretended to be busy in prayer.
When the pious person saw this, he went to inquire of Satan about the prayer that he performed to get the faculty of suspending himself in the atmosphere. But Satan appeared so intently engrossed in prayer that even after repeated calls he did not give any attention to the pious person. Fed up of waiting, the person asked Satan to respond to him under an oath. Satan took a respite from his pretended prayer.
The pious person asked, “What great task you have performed that you are at such an elevated place?” He replied, “I have achieved this status through commitment of a sin. After committing the sin I have repented and done penance.