Nearby ayahs help place verse 14:21 in sequence and meaning.
أَلَمْ تَرَ أَنَّ ٱللَّهَ خَلَقَ ٱلسَّمَـٰوَٰتِ وَٱلْأَرْضَ بِٱلْحَقِّ ۚ إِن يَشَأْ يُذْهِبْكُمْ وَيَأْتِ بِخَلْقٍ جَدِيدٍ
Have you not seen that Allah created the heavens and the earth in truth? If He wills, He can do away with you and produce a new creation.
وَمَا ذَٰلِكَ عَلَى ٱللَّهِ بِعَزِيزٍ
And that is not difficult for Allah.
وَقَالَ ٱلشَّيْطَـٰنُ لَمَّا قُضِىَ ٱلْأَمْرُ إِنَّ ٱللَّهَ وَعَدَكُمْ وَعْدَ ٱلْحَقِّ وَوَعَدتُّكُمْ فَأَخْلَفْتُكُمْ ۖ وَمَا كَانَ لِىَ عَلَيْكُم مِّن سُلْطَـٰنٍ إِلَّآ أَن دَعَوْتُكُمْ فَٱسْتَجَبْتُمْ لِى ۖ فَلَا تَلُومُونِى وَلُومُوٓا۟ أَنفُسَكُم ۖ مَّآ أَنَا۠ بِمُصْرِخِكُمْ وَمَآ أَنتُم بِمُصْرِخِىَّ ۖ إِنِّى كَفَرْتُ بِمَآ أَشْرَكْتُمُونِ مِن قَبْلُ ۗ إِنَّ ٱلظَّـٰلِمِينَ لَهُمْ عَذَابٌ أَلِيمٌ
And Satan will say when the matter has been concluded, "Indeed, Allah had promised you the promise of truth. And I promised you, but I betrayed you. But I had no authority over you except that I invited you, and you responded to me. So do not blame me; but blame yourselves. I cannot be called to your aid, nor can you be called to my aid. Indeed, I deny your association of me [with Allah] before. Indeed, for the wrongdoers is a painful punishment."
وَأُدْخِلَ ٱلَّذِينَ ءَامَنُوا۟ وَعَمِلُوا۟ ٱلصَّـٰلِحَـٰتِ جَنَّـٰتٍ تَجْرِى مِن تَحْتِهَا ٱلْأَنْهَـٰرُ خَـٰلِدِينَ فِيهَا بِإِذْنِ رَبِّهِمْ ۖ تَحِيَّتُهُمْ فِيهَا سَلَـٰمٌ
And those who believed and did righteous deeds will be admitted to gardens beneath which rivers flow, abiding eternally therein by permission of their Lord; and their greeting therein will be, "Peace!"