Tafsir of Ar-Rum 30:59

"Thus" (that is, like that atrocious sealing; and it is permissible that the meaning be: like that speech).

"Does seal" (that is, places a seal) "Allah" (whose majesty is exalted and whose power is immense) "upon the hearts of those who do not know" (that is, those who do not seek knowledge nor investigate the truth, but rather persist in superstitions they have held and nonsense they have innovated. For compound ignorance prevents the perception of truth and necessitates the rejection of the one who speaks the truth. Hence, they said: It is worse than simple ignorance. How subtle is that which was said: The donkey of the sage Thuma said, "If they were fair to me, I would be the one riding, for I am simply ignorant, while my master is compoundly ignorant." Applying "knowledge" to "seeking" is figurative, as it is habitually its necessary consequence. It has been said: The meaning is that Allah the Exalted seals the hearts of those who are not among the people of knowledge—but this is not as strong. The intent of "those who do not know" may possibly be "those who disbelieve," in which case the relative pronoun is used in place of their pronoun to condemn that which is within the scope of the relative clause. It is also possible that it is general, and those [disbelievers] enter into it primarily).

The apparent view of some esteemed scholars leans toward the first possibility. The discussion regarding His—Exalted is He—sealing and stamping of the heart has already preceded.