(They await only but a single Sayhah which will seize them while they are disputing!) meaning, they are only waiting for a single shout which -- and Allah knows best -- will be the trumpet blast of terror when the Trumpet will be blown while the people are in their marketplaces and places of work, arguing and disputing as they usually do. While in this state, Allah will command Israfil to blow into the Trumpet, so he will sound a long note and there will be no one left on the face of the earth except he will tilt his head to listen to the sound coming from heaven. Then the people who are alive will be driven to the gathering place by a fire which will surround them on all sides. Allah says:
In verse 50, it was said فَلَا يَسْتَطِيعُونَ تَوْصِيَةً وَلَا إِلَىٰ أَهْلِهِمْ يَرْجِعُونَ (So they will not be able to make a bequest, nor will they return to their household.), that is, people who are gathered there will not have the respite to make a will among themselves to do something on their behalf, and those who are still outside their houses will not find the respite even to go into their houses. They will lie dead in the very state in which they would be at that time. This is a description of the first blowing of the Horn of the day of Qiyamah as a result of which the entire gamut of the earth and heavens will be destroyed.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 49–52
It has been recorded in the Hadith that the Angel Israfil is looking towards the throne (‘arsh) of God with the trumpet (sur) in his mouth awaiting His orders and ready to blow the trumpet instantly. The blowing of the trumpet will be just like the ringing of a bell which signals the end of the examination. Immediately thereafter, the system of the world will change: the stage of the appearance of results will commence, while at present we are still at the stage of actions.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.