Why is the devil's whispering in the chests, and not heard by the ears?

People generally do not see devils in their true forms nor hear their speech, as devils belong to the unseen world. This is affirmed by Allah’s saying: "Indeed, he sees you, he and his tribe, from where you do not see them." However, Satan may take the form of a human, in which case he can be seen and his speech heard. As for the whispering of Satan in the hearts, it is a reality, for Satan accompanies the heart of the son of Adam. If a person neglects remembrance [of Allah], Satan whispers, and if he remembers Allah, Satan withdraws. This is supported by Allah's saying in Surat An-Nas. Whispering is the casting of falsehood and its beautification into the heart.