Here, Allah (swt) answered the supplication of Prophet Jesus (PBUH). Then, Allah (swt) said:

(  فَمَن يَكْفُرْ بَعْدُ مِنكُمْ فَإِنِّي أُعَذِّبُهُ عَذَابًا لَّا أُعَذِّبُهُ أَحَدًا مِّنَ الْعَالَمِينَ … ) (…but whoever disbelieves afterwards from among you – then indeed will I punish him with a punishment by which I have not punished anyone among the worlds.”): This is because, you, O human being, have seen with your own eyes the miracle which serves as a proof of the Prophet’s truthfulness. So, if you still disbelieve after that, the torment will be harsh and severe.

The Disciples requested a table of food from the Messiah (PBUH). Instead, he replaced their request for it with the request for it to be a sign and celebration for people throughout the ages, which would be proof of the existence of Allah (swt). So, when Allah (swt) said to the Disciples: (“Indeed, I will send it down to you), He also told them after sending it down: (But whoever disbelieves afterwards from among you – then indeed will I punish him with a punishment by which I have not punished anyone among the worlds.”). This is why, we see the Prophet Jesus (PBUH) saying this at the end of the Surah:

  إِن تُعَذِّبْهُمْ فَإِنَّهُمْ عِبَادُكَ ۖ وَإِن تَغْفِرْ لَهُمْ فَإِنَّكَ أَنتَ الْعَزِيزُ الْحَكِيمُ

(If You should punish them – indeed they are Your servants; but if You forgive them – indeed it is You who is the Exalted in Might, the Wise.) (Al-Maida: 118)