The Messenger of Allah (peace be upon him) informed the people that whoever says this invocation Satan will not harm him but shall be in good health and security.
As for his saying: "I seek refuge with the perfect Words of Allah," they mean: I resort to Allah and hold firm with His Way. The one who seeks refuge with Allah will be secure from anything that may harm him because all matters lie in the hands of Allah (Glory be to Him). The perfect words of Allah means: The words which have no defect or shortage such as the words of humans.
As for his saying: "From His Anger and His Punishment," anger is a true quality of Allah (Blessed and Exalted be He) that He described Himself with in His Book and so did the Messenger (peace be upon him) in his Sunnah. Allah (may He be Glorified and Exalted) gets angry, becomes pleased, loves, and hates, as He has many other qualities that were reported in the Qur'an and the Sunnah. The doctrine of Ahl As-Sunnah (those who follow the Sunnah), which is the true doctrine that all people should follow regarding these qualities, is to recognize these qualities as Allah reported in the Qur'an and the Sunnah without distorting, disabling, adapting, or likening these qualities to the qualities of human beings. Ahl As-Sunnah believe that the Ever-Magnificent Lord gets angry, is sought for refuge from His Anger, and fighting desires that may lead to His Anger or entail His Punishment.
Of the things which incur Allah's Wrath and entail His Punishment is that a person resorts to other than Allah in troubles or in the state of fear. How come that a weak person resorts to another weak person for help! How come that a creature resorts to another creature and leaves the Lord of all the Worlds and the Creator of all creation! Here we come to know the shallowness and triviality of the minds of those who go to soothsayers, witches, sorcerers, and foretellers when having troubles or problems to solve. They complain to them their current conditions, seek their needs from them, and ask them to free them from sorrows, ordeals, and terror, in addition to the matter that are not asked except from Allah. Allah (Glory be to Him) says: "Is not He (better than your gods) Who responds to the distressed one, when he calls on Him, and Who removes the evil, and makes you inheritors of the earth, generations after generations? Is there any ilâh (god) with Allâh? Little is that you remember!" [Surat An-Naml: 62]. Is there someone who is able to answer the distressed other than Allah alone?! Is there someone who can reveal the evil and ordeals which inflict man except Allah?! However, only few people who remember this, otherwise they would not have resorted to other than Allah.
As for his saying: "From His Anger and His Punishment," it combines a quality and its effect: The quality is anger and its effect is punishment; we seek refuge with Allah against that.
As for his saying: "and the evil of His People," it means: from all evils that exist in every servant. The meaning of servitude here is the general servitude because all creatures subject to Allah and under His Control as Allah (may He be Exalted) says: "There is none in the heavens and the earth but comes to the Most Gracious (Allâh) as a slave." [Surat Maryam: 93].
As for his saying: "and from the evil insinuations of devils and from their presence (at death)," it means: The insinuations, whispers, and evils of Satan to human beings.
As for his saying: "And from their presence," it means that devils cause evil to people in all conditions. Hence, a person should seek refuge with Allah against the evils of devils and against their presence.
So, how great invocation this is, how very effective it is, and how inclusive it is to protect a person from anything that may cause fear and horror to him. May Allah grant us success!