لَتَرْكَبُنَّ طَبَقًا عَن طَبَقٍۢ
Sentence structure
لَ introduces the oath response. تَرْكَبُ is a second-person masculine-plural imperfect: its subject-wāw is omitted before the heavy emphatic نَّ. طَبَقًا is accusative; عَن طَبَقٍ has more than one accepted local attachment.
Ayah summary
Human beings will pass stage by stage from this world through death and Barzakh to the Resurrection.
لَتَرْكَبُنَّ — You will surely embark
Grammar: لَ marks the oath response; تَرْكَبُ is a second-person masculine-plural imperfect whose subject-wāw is omitted before the heavy emphatic نَّ.
طَبَقًا — (to) stage
Grammar: An indefinite accusative noun; it is taught here as the object.
عَن — from
Grammar: A preposition; عَن طَبَقٍ may describe طَبَقًا or function circumstantially, so one attachment is not imposed.
طَبَقٍۢ — stage
Grammar: An indefinite genitive noun governed by عَن.