The Repentance
فَأَعْقَبَهُمْ نِفَاقًا فِى قُلُوبِهِمْ إِلَىٰ يَوْمِ يَلْقَوْنَهُۥ بِمَآ أَخْلَفُوا۟ ٱللَّهَ مَا وَعَدُوهُ وَبِمَا كَانُوا۟ يَكْذِبُونَ
So He penalized them with hypocrisy in their hearts until the Day they will meet Him - because they failed Allah in what they promised Him and because they [habitually] used to lie.
Nearby ayahs help place verse 9:77 in sequence and meaning.
۞ وَمِنْهُم مَّنْ عَـٰهَدَ ٱللَّهَ لَئِنْ ءَاتَىٰنَا مِن فَضْلِهِۦ لَنَصَّدَّقَنَّ وَلَنَكُونَنَّ مِنَ ٱلصَّـٰلِحِينَ
And among them are those who made a covenant with Allah, [saying], "If He should give us from His bounty, we will surely spend in charity, and we will surely be among the righteous."
فَلَمَّآ ءَاتَىٰهُم مِّن فَضْلِهِۦ بَخِلُوا۟ بِهِۦ وَتَوَلَّوا۟ وَّهُم مُّعْرِضُونَ
But when he gave them from His bounty, they were stingy with it and turned away while they refused.
أَلَمْ يَعْلَمُوٓا۟ أَنَّ ٱللَّهَ يَعْلَمُ سِرَّهُمْ وَنَجْوَىٰهُمْ وَأَنَّ ٱللَّهَ عَلَّـٰمُ ٱلْغُيُوبِ
Did they not know that Allah knows their secrets and their private conversations and that Allah is the Knower of the unseen?
ٱلَّذِينَ يَلْمِزُونَ ٱلْمُطَّوِّعِينَ مِنَ ٱلْمُؤْمِنِينَ فِى ٱلصَّدَقَـٰتِ وَٱلَّذِينَ لَا يَجِدُونَ إِلَّا جُهْدَهُمْ فَيَسْخَرُونَ مِنْهُمْ ۙ سَخِرَ ٱللَّهُ مِنْهُمْ وَلَهُمْ عَذَابٌ أَلِيمٌ
Those who criticize the contributors among the believers concerning [their] charities and [criticize] the ones who find nothing [to spend] except their effort, so they ridicule them - Allah will ridicule them, and they will have a painful punishment.