Bismillah
as salam alykom
Can I step in for a moment?
Ok as for how come mankind is weak versus shaytan's inspirtation specially when FHC quoted the alleged satanic verses, FHC pls search on this site, Insh aAllah u will come up with full explanation on this issue, you will be surprised, although I m not expecting u to accept the explantion, that is no problem. My role is to provide the explanation not to force u to accept it.
Bottom line, Mohamed prayer and peace be upon him was never decieved by shaytan, never uttered a word thru a satanic inspiration, quran is well protected Alhamdulelah, it didnt contain satanic versus that were abrogated. Check the abrogation thread.
Now, having said that, let us continue.
Mankind is subject to two sources of evil, not only satan but the self as well.
Mankind and jin do have free will thus they must be tested, they will be judged, unlike angles. Satan is the obligatory question.
Any devout muslims shall never go on without making a sin, u know why? because it is mandatroy for Allah's Name and Attribute (since u r a native arabic speaker) Attawab, Al Ghafour, Al Ghaffar, to continue functioning till the Day After. if no one sins, then no one asks for forgiveness, or repentance those Names and Attributes shall be constant. Plus it is part of the worship which we choose to carry out or not, I mean we get rewarded for fulfilling this optional worship.
Hope i added something.
