﴿ لِّكُلِّ نَبَإٍۢ مُّسْتَقَرٌّۭ ۚ وَسَوْفَ تَعْلَمُونَ ﴾

“Every tiding [from God] has a term set for its fulfilment: and in time you will come to know [the truth]."”

Every tiding every announcement has a conclusion a fixed time in which it will take place and be concluded including the tiding concerning your punishment. And you will come to know’ — this is a threat for them.