Tafsir of Al-Mursalat 77:14

"And what will make you realize what the Day of Decision is?" That is: what thing has made you aware of what it is?

The first "ma" (what) is the subject (mubtada') and "adraka" (made you realize) is the predicate (khabar). The second "ma" is a fronted predicate and "yawm al-fasl" (the Day of Decision) is the delayed subject. It is not the other way around, as Sibawayh chose, because the focus of the benefit lies in clarifying that the Day of Decision is an astounding matter whose magnitude cannot be measured and whose essence cannot be fathomed. This is what the predicative nature of "ma" indicates, rather than clarifying that the Day of Decision is one of the astounding matters, as the reverse would indicate. The use of the explicit noun in place of a pronoun is to increase the sense of horror and intimidation intended by the discourse.