[Pooya/Ali Commentary 73:5] Qawlan thaqila, (weighty word) is the Quran. The Holy Prophet has used the word thaqalayn to refer to the Quran and his Ahl ul Bayt-two weighty things. Refer to page 6, and commentary of Baqarah: 2 and Ya Sin: 12. Aqa Mahdi Puya says: The responsibility to guide mankind described as weighty in this verse has been referred to as a burden in Inshirah: 2 for which he needed a supporter as Musa had Harun to assist him (see commentary of Ta Ha: 9 to 98)-as verses 15 and 16 of this surah imply and infer.