Calls, Announcements and Warnings. The Trumpet Blasts
These momentous and earth shaking events, which in many ways are calamitous (specially for the unbelievers), are to be preceded by warnings and announcements and soundings of the trumpet :
[50:41-2]: And listen for the Day when the Caller will call out from a place quiet near,- The Day when they will hear a (mighty) Blast in (very) truth: that will be the Day of Resurrection.
Who would be this Caller, and where is this place that is quite near?
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[8:24] : O ye who believe! Obey Allah, and the messenger when He calleth you to that which quickeneth you, and know that Allah cometh in between the man and his own heart, and that He it is unto Whom ye will be gathered.
[34:28] :"We have not sent thee (Muhammad) but to the whole of mankind, as a giver of glad tidings and as a warner, but most of mankind still do not know."
Part of the warning is to bring people back to the religion of God, to the Straight Path*, after they have divided themselves into factions and sects which, "disown each other and curse each other" [29:25].
* The Straight Path, which is narrower than a hair and sharper than a sword is explained in this verse:
[6:161] : Say: Lo! As for me, my Lord hath guided me unto a straight path, a right religion, the community of Abraham, the upright, who was no idolater.
It may be of interest that in the very first sura of the Qur'an (the opening chapter, Al-Fatiha) , the word "Deen" which translates to religion, creed, faith, is used to tell us about the "Day of Judgment" (Yawmul Deen).
A warning to precede the penalty, is indicative of God's mercy and justice :
[11:117] : Nor would thy Lord be the One to destroy communities for a single wrong-doing, if its members were likely to mend.
[20:134] : And if We had inflicted on them a penalty before this, they would have said: "Our Lord! If only Thou hadst sent us a messenger, we should certainly have followed Thy Signs before we were humbled and put to shame."
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[17:15] : Whoever goes aright, for his own soul does he go aright; and
whoever goes astray, to its detriment only does he go astray: nor can
the bearer of a burden bear the burden of another, nor do We chastise
until We raise an apostle.
Another way to see this may be argued, that if we have eyes to recognize the calamities and the suffering, and the disunity and contention all around us, we might ask ourselves if there has been a warning that we neglected to heed.