Tafsir of Ya seen 36:53

(It was not) — meaning, the action or the blast that was mentioned previously was not — (but a single blast) that occurred from the blowing of Israfil, peace be upon him, into the Trumpet. It has been said: It is the command of Israfil, peace be upon him, saying, "O decayed bones, disjointed limbs, and torn hair! Indeed, Allah commands you to gather for the final judgment." It was also recited with the nominative case (raf') for sayḥatun (a single blast), and its grammatical justification has already been addressed.

(Then behold, they are all) — gathered — (brought before Us) — meaning, present before Us and in the place of Our decree, where the apparent exercise of power by anyone else has ceased — (for the judgment of the account) without even the delay of a blinking eye. In this is a manifestation of the ease of the affair of resurrection and the gathering, and an indication that they are independent of any [intermediary] causes, in a manner that is not hidden.