وَالَّذِينَ كَفَرُوا فَتَعْسًا لَّهُمْ
...
But as for those who disbelieve -- misery awaits them,
This misery is the opposite of making firm the footholds of the believers who support the cause of Allah and His Messenger.
It has been confirmed in a Hadith that Allah's Messenger said,
تَعِسَ عَبْدُالدِّينَارِ تَعِسَ عَبْدُالدِّرْهَمِ تَعِسَ عَبْدُالْقَطِيفَةِ تَعِسَ وَانْتَكَسَ وَإِذَا شِيكَ فَلَ انْتَقَش
Misery awaits the servant of the Dinar; misery awaits the servant of the Dirham; misery awaits the servant of velvet. Misery awaits him, and degeneracy; and if he is pricked by a thorn, may he not find anyone to pull it for him.
This means may Allah not cure him.
Then Allah says,
...
وَأَضَلَّ أَعْمَالَهُمْ
and (Allah) will make their deeds vain.
meaning, He will nullify them and make them fruitless.
Thus, Allah says,