Ibn Kathir (Abridged)
Hafiz Ibn KathirThe Whispering of Shaytan and the People of Taqwa
Allah mentions His servants who have Taqwa, obeying His orders, and avoid what He forbade: إِذَا مَسَّهُمْ(when comes to them) an evil thought, or anger, or the whispers of Shaytan cross their mind, or intend to err, or commit an error, تَذَكَّرُواْ(they remember) Allah's punishment, as well as, His tremendous reward. They remember Allah's promises and threats, then repent, go back to Him, seek refuge with Him and ask for forgiveness before death, فَإِذَا هُم مُّبْصِرُونَ(and (indeed) they then see (aright)) they become aright and aware of the error of their ways. A Brethren of Devils among Mankind lure to Falsehood
Allah said next, وَإِخْوَنُهُمْ يَمُدُّونَهُمْ(But (as for) their brothers they plunge them deeper) in reference to the devils' brothers among mankind. Allah said in another Ayah, إِنَّ الْمُبَذرِينَ كَانُواْ إِخْوَنَ الشَّيَـطِينِ(Verily, the spendthrifts are brothers of the Shayatin) 17:27 for they are followers of the Shayatin, who listen to them and obey their orders. يَمُدُّونَهُمْ فِى الْغَىِّ(They plunge them deeper into error) the devils help them commit sins, making this path easy and appealing to them ثُمَّ لاَ يُقْصِرُونَ(and they never stop short) for the devils never cease inciting mankind to commit errors. `Ali bin Abi Talhah reported that Ibn `Abbas commented on Allah's statement, وَإِخْوَنُهُمْ يَمُدُّونَهُمْ فِى الْغَىِّ ثُمَّ لاَ يُقْصِرُونَ (But (as for) their brothers they plunge them deeper into error, and they never stop short.) "Neither mankind stop short of the evil that they are doing nor the devils stop short of luring them. " Therefore, لاَ يُقْصِرُونَ(they never stop short) refers to the devils getting tired or stopping their whispering.
Allah said in another Ayah, أَلَمْ تَرَ أَنَّآ أَرْسَلْنَا الشَّيَـطِينَ عَلَى الْكَـفِرِينَ تَؤُزُّهُمْ أَزّاً (See you not that We have sent Shayatin against the disbelievers to push them to do evil) 19:83 persistently luring the disbelievers to commit evil, according to Ibn `Abbas and others.