إِنَّ الْإِنْسَانَ لِرَبِّهِ لَكَنُودٌ
Truly the human being is profoundly ungrateful toward his Lord. (100:6)
This is the response to the preceding oath. Inna and the emphatic lām reinforce the assertion. Fronting li-rabbihi foregrounds the very relationship in which ingratitude is reprehensible: the person’s duty toward the Lord who provides. Kanūd conveys marked thanklessness.
Generic al-insān describes a human propensity; it does not require that every individual at all times exhibit it. The passage shifts from a vivid oath scene to a moral judgment, and the emphatic answer gives the opening imagery its argumentative destination.