Surah Al-Muzzammil 73:5

إِنَّا سَنُلْقِى عَلَيْكَ قَوْلًا ثَقِيلًا

Indeed, We will cast upon you a heavy word.

Translation: Saheeh International

Tafsir

Verily soon We shall cast on you a weighty an awe-inspiring or stern word a weighty Qur’ān because of the prescriptions imposed in it.

Excerpt from Tafsir al-Jalalayn, commentary on 73:5, via Quran.com. The reader has the full commentary and 9 more tafsirs.