Tafsir of Al-Hijr 15:12

"Likewise do We insert it into..."

"Likewise," that is, just as We inserted into the hearts of those who mocked their messengers and what they brought, so do We insert it—meaning, We cause it to enter. It is said: "I threaded (salaktu) the needle," and "the spear point (al-sinan) into the one stabbed (al-mat'un)," as Abu 'Ubaydah mentioned, in the same sense. The pronoun, according to a group—including al-Hasan, as mentioned by al-Ghaznawi—refers to the Reminder (the Qur'an): "into the hearts of the criminals."

This refers to the people of Mecca or the category of criminals in general, such that they enter into it as the primary recipients. The meaning of "the insertion" being accompanied by mockery, rendering it unacceptable due to what wisdom dictates, is that Allah, Exalted is He, casts the Qur'an into the hearts of the criminals while it is mocked and unacceptable, because they are among the people of abandonment and possess no entitlement to accept the truth—just as the Glorified One cast the books of the messengers, peace be upon them, into the hearts of the sects of the ancients while they were mocked and unacceptable for the same reason. The present tense form is used because the object of comparison (al-mushabbah bihi) preceded it in existence, which is the insertion that occurred among the sects of the first generations.