The Believer and the Rebellious are not equal

Allah tells us that in His justice and generosity, on the Day of Judgement He will not judge those who believed in His signs and followed His Messengers, in the same way as He will judge those who rebelled, disobeyed Him and rejected the Messengers sent by Allah to them. This is like the Ayat:

أَمْ حَسِبَ الَّذِينَ اجْتَرَحُواْ السَّيِّئَـتِ أَن نَّجْعَلَهُمْ كَالَّذِينَ ءَامَنُواْ وَعَمِلُواْ الصَّـلِحَـتِ سَوَآءً مَّحْيَـهُمْ وَمَمَـتُهُمْ سَآءَ مَا يَحْكُمُونَ

Before approaching verse 16: تَـتَجَافٰى جُنُوْبُهُمْ عَنِ الْمَضَاجِعِ يَدْعُوْنَ رَبَّهُمْ خَوْفًا وَّطَمَعًا (Their sides remain apart from their beds. They call their Lord with fear and hope - 16), it should be borne in mind that disbelievers, Mushriks and the deniers of the day of Qiyamah were warned in the verses previous to it. After that, starting from: اِنَّمَا يُؤْمِنُ بِاٰيٰتِنَا ! (Only those people believe in Our verses - 15) mentioned there are special attributes of sincere believers and the high ranks reserved for them. Pointed to in the cited verse is one such attribute of these believers: They leave the comfort of their beds, rise and get busy with the remembrance of Allah in submission and supplication - because, they are apprehensive of His displeasure and punishment while remaining hopeful of His mercy and reward. This very combination of fear and hope keeps them returning to Dhikr and Du'a' repeatedly, anxiously and animated at the same time.

The Salah of Tahajjud