ثُمَّ كَلَّا سَوْفَ تَعْلَمُونَ ٤
Sentence structure
ثُمَّ coordinates with sequence. كَلَّا deters, سَوْفَ marks the future, and تَعْلَمُونَ is a second-person masculine-plural imperfect.
Ayah summary
Again, never so; you will soon come to know the reality.
ثُمَّ — Then
Grammar: A conjunction indicating ordered sequence with an interval.
كَلَّا — No indeed
Grammar: A deterrent particle that rejects and warns.
سَوْفَ — soon will
Grammar: A future particle before an imperfect verb.
تَعْلَمُونَ — you will know
Grammar: A second-person masculine-plural imperfect; واو الجماعة is the subject, final نَ marks the indicative form, and its object is omitted without specifying an unstated wording.