فَاِنَّمَا هِيَ زَجْرَةٌ وَّاحِدَةٌ فَاِذَا هُمْ يَنْظُرُوْنَ ( الصافات: ١٩ )
fa-innamā
فَإِنَّمَا
Then only
hiya
هِىَ
it
zajratun
زَجْرَةٌ
(will be) a cry
wāḥidatun
وَٰحِدَةٌ
single
fa-idhā
فَإِذَا
then behold!
hum
هُمْ
They
yanẓurūna
يَنظُرُونَ
will see
Fa innamaa hiya zajra tunw waahidatun fa izaa hum yanzuroon (aṣ-Ṣāffāt 37:19)
Sahih International:
It will be only one shout, and at once they will be observing. (As-Saffat [37] : 19)
1 Mufti Taqi Usmani
So, it will be only a single castigating call, and all of a sudden they will begin to see.