{Indeed, the seizing of your Lord} means the punishment of your Lord {is severe}.
Muhammad said: (Indeed, the seizing of your Lord is severe) is the response to the oath (By the sky containing constellations).
﴿إِن بَطش رَبك﴾ عُقُوبَة رَبك ﴿لشديد﴾.
قَالَ مُحَمَّدٌ: (إِنَّ بَطْشَ رَبِّكَ لشديد) هُوَ جَوَابُ الْقَسَمِ (وَالسَّمَاءِ ذَاتِ الْبُرُوجِ).