They say: "Allah has begotten a son." Glory is to Him! He is Rich (free of all needs). His is all that is in the heavens and all that is in the earth. No warrant have you for this. Do you say against Allah what you know not (68)Say: "Verily, those who invent a lie against Allah will never be successful. (69)(A brief) enjoyment in this world! and then unto Us will be their return, then We shall make them taste the severest torment because they used to disbelieve (70)

Allah criticizes those who claim that He has,

وَلَدًا ۗ سُبْحَانَهُ ۖ هُوَ الْغَنِيُّ

(...begotten a son. Glory is to Him! He is Rich (Free of all needs).) He is Greater than that and above it. He is Self-Sufficient, free of want or need of anything. Everything else is in desperate need of Him,

لَهُ مَا فِي السَّمَاوَاتِ وَمَا فِي الْأَرْضِ

(His is all that is in the heavens and all that is in the earth.) So how can He have a son from what He has created Everything and everyone belongs to Him and is His servant.

إِنْ عِندَكُم مِّن سُلْطَانٍ بِهَٰذَا

(No warrant have you for this) Meaning, you have no proof for the lies and falsehood that you claim,

أَتَقُولُونَ عَلَى اللَّهِ مَا لَا تَعْلَمُونَ

(Do you say against Allah what you know not.) This is a severe threat and a firm warning. Similarly, Allah threatened and said:

وَقَالُوا اتَّخَذَ الرَّحْمَٰنُ وَلَدًا - لَّقَدْ جِئْتُمْ شَيْئًا إِدًّا - تَكَادُ السَّمَاوَاتُ يَتَفَطَّرْنَ مِنْهُ وَتَنشَقُّ الْأَرْضُ وَتَخِرُّ الْجِبَالُ هَدًّا - أَن دَعَوْا لِلرَّحْمَٰنِ وَلَدًا - وَمَا يَنبَغِي لِلرَّحْمَٰنِ أَن يَتَّخِذَ وَلَدًا - إِن كُلُّ مَن فِي السَّمَاوَاتِ وَالْأَرْضِ إِلَّا آتِي الرَّحْمَٰنِ عَبْدًا - لَّقَدْ أَحْصَاهُمْ وَعَدَّهُمْ عَدًّا - وَكُلُّهُمْ آتِيهِ يَوْمَ الْقِيَامَةِ فَرْدًا

(And they say: "The Most Gracious has begotten a son." Indeed you have brought forth a terribly evil thing. Whereby the heavens are almost torn, and the earth is split asunder, and the mountains fall in ruins, that they ascribe a son to the Most Gracious. But it is not suitable for the Most Gracious that He should beget a son. There is none in the heavens and the earth but comes unto the Most Gracious as a servant. Verily, He knows each one of them, and has counted them a full counting. And everyone of them will come to Him alone on the Day of Resurrection.)(19:88-95)

Then Allah warned the liars that fabricated the claim that He has begotten a son. He warned that they will not succeed, never prospering in this world or in the Hereafter. In this world Allah will lead them, step-by-step, to their ruin. He will give them respite and put up with them for a while. He will allow them to have little enjoyment,

ثُمَّ نَضْطَرُّهُمْ إِلَىٰ عَذَابٍ غَلِيظٍ

(then in the end We shall oblige them to (enter) a great torment.)(31:24) As Allah said here:

مَتَاعٌ فِي الدُّنْيَا

((A brief) enjoyment in this world!) meaning, only a short period,

ثُمَّ إِلَيْنَا مَرْجِعُهُمْ

(and then unto Us will be their return) on the Day of Resurrection;

ثُمَّ نُذِيقُهُمُ الْعَذَابَ الشَّدِيدَ بِمَا كَانُوا يَكْفُرُونَ

(Then We shall make them taste the severest torment because they used to disbelieve.) meaning, 'We shall make them taste the painful punishment because of their Kufr and lies about Allah.'