Allah states that He allowed Adam and his wife to dwell in Paradise and to eat from all of its fruits, except one tree. We have already discussed this in Surat Al-Baqarah. Thus, Shaytan envied them and plotted deceitfully, whispering and suggesting treachery. He wished to rid them of the various favors and nice clothes that they were enjoying.
(He (Shaytan) said) uttering lies and falsehood,
("Your Lord did not forbid you this tree save you should become angels...") meaning, so that you do not become angels or dwell here for eternity. Surely, if you eat from this tree, you will attain both, he said. In another Ayah,
(Shaytan whispered to him, saying: "O Adam! Shall I lead you to the Tree of Eternity and to a kingdom that will never waste away") 20:120. Here, the wording is similar, so it means, `so that you do not become angels' as in;
((Thus) does Allah make clear to you (His Law) lest you go astray. ) 4:176 meaning, so that you do not go astray, and,
(And He has affixed into the earth mountains standing firm, lest it should shake with you;) 16:15 that is, so that the earth does not shake with you.
(And he Qasamahuma), swore to them both by Allah, saying,
("Verily, I am one of the sincere well-wishers for you both.") for I was here before you and thus have better knowledge of this place. It is a fact that the believer in Allah might sometimes become the victim of deceit. Qatadah commented on this Ayah, "Shaytan swore by Allah, saying, `I was created before you, and I have better knowledge than you. Therefore, follow me and I will direct you."'