Tafsir of Al-Muddathir 74:18

It is an explanation for the threat and his deserving of it, or an elucidation of his stubbornness regarding the verses of the Almighty, Exalted is He; thus, the sentence serves as an interpretation of that, having no place in inflection, while what is between them is a parenthetical clause. It has also been said that the sentence upon him is a substitute (badal) for His saying, Exalted is He, "Indeed, he has been towards Our verses stubborn," meaning: he pondered what he would say regarding the Qur’an and determined within himself what he would say.