Surah Al-A'raaf (7) — Ayah 21

(Ayah 21){ وَ قَاسَمَهُمَاۤ:} The verb form "Mufa'alah" (Muqasamah) is used for mutual confrontation from both sides. Here, only Satan swore an oath; Adam (peace be upon him) did not swear any oath in response. Therefore, here it is for emphasis, so the translation is "swore repeatedly."

21. 1. Regarding the blessings and comforts of Paradise that were granted to Adam (علیہ السلام) and Hawwa, Shaytan enticed both of them and lied that Allah does not want to keep you in Paradise forever, that is why He has forbidden you from eating the fruit of this tree, because its effect is that whoever eats it becomes an angel or attains eternal life. Then, by swearing, he also showed himself to be their well-wisher, which influenced Adam (علیہ السلام) and Hawwa. That is why the friends of Allah are easily deceived in the name of Allah.

Then he swore to them, "Indeed, I am a sincere advisor [17] to you."

[17]
The Ways in Which Satan Leads Humans Astray:

In these two verses, light has been shed on the method by which Satan leads humans astray. This method begins with Satan instilling a whisper in the human heart, and by whisper is meant every thought whose implementation results in disobedience to a command of Allah, that is, Satan’s first attack to mislead a human is on his thoughts, as the Messenger of Allah ﷺ said that Satan runs through the veins of a human just as blood runs. [بخاري۔ كتاب بدء الخلق۔ باب صفة ابليس و جنوده]
(2) Satan never misleads a human by showing him an evil path, nor can he do so; rather, he always misleads by showing alluring prospects. For example, if you do this, your condition can become much better than it is now, and by doing such and such, your business can greatly prosper, and so on. Thus, he showed alluring prospects to our master Adam and Hawwa (peace be upon them) as well, saying that if you eat from this tree, you will become like angels or become angels, and then there will be no question of you being expelled from this Paradise.
(3) Iblis or his followers not only show alluring prospects but also instill various arguments in the heart, assuring him that the path shown is truly for his betterment and goodwill, and that there is no personal interest in it for them; and for this assurance, if he has to swear oaths, he does so repeatedly.
(4) Satan’s very first target is the sexual organs of humans; the easiest way to mislead a human is to open the doors of obscenity and make him wayward in sexual matters. That is, the natural sense of modesty and shame that Allah has placed in humans, Satan weakens this sense. The method of Iblis and his followers remains unchanged to this day: in the eyes of such people, no work of cultural or civilizational progress can even begin until they bring women out into the marketplace by making them immodest and open all avenues of free mixing between men and women. For such people, a woman staying at home to care for her children is called a prison, and the veil is considered the greatest obstacle to progress, and all this is from the tricks taught by Satan. And the notion that Satan first misled Hawwa ؑ and then, at her suggestion, our master Adam ؑ also ate the fruit of that tree, is probably taken from Isra’iliyat; there is no explicit mention of this in the Book and Sunnah. From the Quran, it is clear that Satan made promises and threats to both, and both were deceived by him. Here the question arises: when Allah had forbidden our master Adam ؑ and Hawwa from approaching that tree, how did they fall into Satan’s trap? The answer is that many years had passed while Adam and Hawwa were living in comfort in Paradise, and they never even thought of approaching that tree. Eventually, they forgot Allah’s command, and at that time, Satan found the opportunity to incite them to disobedience. As is clear from this verse of the Noble Quran, verse ﴿فَنَسِيَ وَلَمْ نَجِدْ لَهٗ عَزْمًا﴾ [طه: 115] “Then Adam ؑ forgot the command of Allah, and We did not find in him any intention of disobedience.”