(… السَّمَاءُ مُنفَطِرٌ بِهِ ) (The heaven will break apart therefrom; …): The sky, in spite of its tremendousness, will split and crack on the Day of Judgement. So, what will be the case with other creatures? Allah (swt) informs us that on this horrible Day the sky will split into small parts and stars will fall down. Allah (swt) says:

 إِذَا السَّمَاءُ انفَطَرَتْ

(When the sky breaks apart) (Al-Infitar: 1)

Despite its sturdiness, the sky will fall into small pieces.

(… مُنفَطِرٌ بِهِ… ) (…will break apart therefrom …): The sky will break apart by Allah’s Command. We note that Allah (swt) uses a masculine form to refer to the sky despite that the Arabic word of (sky) ia a feminine noun. It is put in the masculine form for it denotes a ceiling as in Allah (swt) saying:

 وَجَعَلْنَا السَّمَاءَ سَقْفًا مَّحْفُوظًا

(And We made the sky a protected ceiling, but they, from its signs, are turning away) (Al-Anbiya: 32)

In another verse, Allah (swt) points to the split of the sky, saying:

 وَيَوْمَ تَشَقَّقُ السَّمَاءُ بِالْغَمَامِ وَنُزِّلَ الْمَلَائِكَةُ تَنزِيلًا

(And [mention] the Day when the heaven will split open with [emerging] clouds, and the angels will be sent down in successive descent) (Al-Furqan: 25)

Some exegetes say that the sky will split open with emerging clouds and the Angels will descend from its cracks. The clouds are also mentioned in the following verse:

 هَلْ يَنظُرُونَ إِلَّا أَن يَأْتِيَهُمُ اللَّهُ فِي ظُلَلٍ مِّنَ الْغَمَامِ وَالْمَلَائِكَةُ

(Do they await but that Allah should come to them in covers of clouds and the angels) (Al-Baqara: 210)

(… مُنفَطِرٌ بِهِ… ) (…break apart therefrom …): Meaning, disordered splitting. As for the Arabic pronoun of (therefrom), Al-Munther and other some exegetes said that it refers to the Day of Resurrection, while Mujahed said that it refers to Allah (swt).  

(  كَانَ وَعْدُهُ مَفْعُولًا… ) (…ever is His promise fulfilled): Allah’s Promise will inevitably come to pass as He is the Omnipotent Who has all the Attributes of Grandeur and Perfection, unlike people’s promises which may not be fulfilled.