Basically...

Basically, the devilish ones act hiddenly, and sometimes they murmur temptations into our ears so that we believe that the ideas are our own thoughts. This very kind of thinking causes us to go astray. The method of Satan is alluring and shows injustice in the form and under the guise of justice; lies inside a shell of truth; sin in the semblance of worship, and aberration in the appearance of guidance.

In short, they, themselves, and their affairs, both, are hidden, and this is a warning to all followers, of the right and the path of truth, not to expect to see Satans in their real form, or observe their activities in their true, crooked shape, No it will never be so. They are 'slinking whisperers' and their job is to plot, lie, be mischievous, be hypocritical, commit fraud and deceit, simulating truth, and hiding the right.

If they appear on the scene in their real form, if they do not mix wrong with right, and if they speak clearly and honestly, the truth would become apparent; as Hazrat Ali (as) says: “The fact is, had falsehood been allowed to appear separately from truth, seekers of truth would have easily discerned it and would have kept away from falsehood...” [^4] They always take parts of truth and falsehood and mix them together to get control over people; as Amir-al-Mo'mineen Ali (as), continuing the above sermon, says: “...and Satan took advantage of this situation and gained complete control over the minds of its followers.” [^5] The words 'whispers' and 'hearts' used in the verse: "Who whispers evil into the hearts of Mankind" are an emphasis on this idea.

All of these are on the one hand, and on the other hand the phrase: "From Jinn and Mankind" informs us that 'the slinking whisperer' is not among only a group of people or a special class of Man with a particular sign, but they can be found here and there among Jinn and Man with any form and in any society. We should be careful of them and take refuge with Allah from the evil of all of them. Explanation: Why Do We Take Refuge With Allah?

At any moment it is possible that one may go astray, and when Allah bids His Apostle to take refuge with the Lord from the evil of the 'slinking whisperer', it is an evidence that becoming involved in the trap of the tempters, who whisper evil in people's minds, is possible. So, everyone must seek refuge to Allah, with His name /rabb/, i.e., the Lord of Man, i.e., the Cherisher and Sustainer.