لِّكُلِّ نَبَإٍ مُّسْتَقَرٌّ
...
For every news there is a reality...,
According to Ibn Abbas and others,
meaning, for every news, there is a reality, in that, this news will occur, perhaps after a while.
Allah said in other Ayat,
وَلَتَعْلَمُنَّ نَبَأَهُ بَعْدَ حِينِ
And you shall certainly know the truth of it after a while. (38:88)
and,
لِكُلِّ أَجَلٍ كِتَابٌ
(For) each and every matter there is a decree (from Allah). (13:38)
This, indeed, is a warning and a promise that will surely occur,
...
وَسَوْفَ تَعْلَمُونَ
and you will come to know.
Allah's statement,